Time Realization and Distribution Group

<!DOCTYPE html> <html lang="en" dir="ltr" prefix="content: http://purl.org/rss/1.0/modules/content/ dc: http://purl.org/dc/terms/ foaf: http://xmlns.com/foaf/0.1/ og: http://ogp.me/ns# rdfs: http://www.w3.org/2000/01/rdf-schema# schema: http://schema.org/ sioc: http://rdfs.org/sioc/ns# sioct: http://rdfs.org/sioc/types# skos: http://www.w3.org/2004/02/skos/core# xsd: http://www.w3.org/2001/XMLSchema# "> <head><script type="text/javascript" src="/_static/js/bundle-playback.js?v=HxkREWBo" charset="utf-8"></script> <script type="text/javascript" src="/_static/js/wombat.js?v=txqj7nKC" charset="utf-8"></script> <script>window.RufflePlayer=window.RufflePlayer||{};window.RufflePlayer.config={"autoplay":"on","unmuteOverlay":"hidden"};</script> <script type="text/javascript" src="/_static/js/ruffle/ruffle.js"></script> <script type="text/javascript"> __wm.init("https://web.archive.org/web"); __wm.wombat("https://www.nist.gov/pml/time-and-frequency-division/time-services","20231209224628","https://web.archive.org/","web","/_static/", "1702161988"); </script> <link rel="stylesheet" type="text/css" href="/_static/css/banner-styles.css?v=S1zqJCYt" /> <link rel="stylesheet" type="text/css" href="/_static/css/iconochive.css?v=3PDvdIFv" />  <meta charset="utf-8"/><script type="text/javascript">(window.NREUM||(NREUM={})).init={ajax:{deny_list:["gov-bam.nr-data.net"]}};(window.NREUM||(NREUM={})).loader_config={licenseKey:"37b7ccb661",applicationID:"1089704227"};;/*! For license information please see nr-loader-rum-1.248.0.min.js.LICENSE.txt */ (()=>{var e,t,n={234:(e,t,n)=>{"use strict";n.d(t,{P_:()=>h,Mt:()=>m,C5:()=>s,DL:()=>w,OP:()=>j,lF:()=>R,Yu:()=>_,Dg:()=>v,CX:()=>c,GE:()=>A,sU:()=>T});var r=n(8632),i=n(9567);const a={beacon:r.ce.beacon,errorBeacon:r.ce.errorBeacon,licenseKey:void 0,applicationID:void 0,sa:void 0,queueTime:void 0,applicationTime:void 0,ttGuid:void 0,user:void 0,account:void 0,product:void 0,extra:void 0,jsAttributes:{},userAttributes:void 0,atts:void 0,transactionName:void 0,tNamePlain:void 0},o={};function s(e){if(!e)throw new Error("All info objects require an agent identifier!");if(!o[e])throw new Error("Info for ".concat(e," was never set"));return o[e]}function c(e,t){if(!e)throw new Error("All info objects require an agent identifier!");o[e]=(0,i.D)(t,a);const n=(0,r.ek)(e);n&&(n.info=o[e])}const u=e=>{if(!e||"string"!=typeof e)return!1;try{document.createDocumentFragment().querySelector(e)}catch{return!1}return!0};var d=n(7056),l=n(50);const f=()=>{const e={mask_selector:"*",block_selector:"[data-nr-block]",mask_input_options:{color:!1,date:!1,"datetime-local":!1,email:!1,month:!1,number:!1,range:!1,search:!1,tel:!1,text:!1,time:!1,url:!1,week:!1,textarea:!1,select:!1,password:!0}};return{feature_flags:[],proxy:{assets:void 0,beacon:void 0},privacy:{cookies_enabled:!0},ajax:{deny_list:void 0,block_internal:!0,enabled:!0,harvestTimeSeconds:10,autoStart:!0},distributed_tracing:{enabled:void 0,exclude_newrelic_header:void 0,cors_use_newrelic_header:void 0,cors_use_tracecontext_headers:void 0,allowed_origins:void 0},session:{domain:void 0,expiresMs:d.oD,inactiveMs:d.Hb},ssl:void 0,obfuscate:void 0,jserrors:{enabled:!0,harvestTimeSeconds:10,autoStart:!0},metrics:{enabled:!0,autoStart:!0},page_action:{enabled:!0,harvestTimeSeconds:30,autoStart:!0},page_view_event:{enabled:!0,autoStart:!0},page_view_timing:{enabled:!0,harvestTimeSeconds:30,long_task:!1,autoStart:!0},session_trace:{enabled:!0,harvestTimeSeconds:10,autoStart:!0},harvest:{tooManyRequestsDelay:60},session_replay:{autoStart:!0,enabled:!1,harvestTimeSeconds:60,sampling_rate:50,error_sampling_rate:50,collect_fonts:!1,inline_images:!1,inline_stylesheet:!0,mask_all_inputs:!0,get mask_text_selector(){return e.mask_selector},set mask_text_selector(t){u(t)?e.mask_selector=t+",[data-nr-mask]":null===t?e.mask_selector=t:(0,l.Z)("An invalid session_replay.mask_selector was provided and will not be used",t)},get block_class(){return"nr-block"},get ignore_class(){return"nr-ignore"},get mask_text_class(){return"nr-mask"},get block_selector(){return e.block_selector},set block_selector(t){u(t)?e.block_selector+=",".concat(t):""!==t&&(0,l.Z)("An invalid session_replay.block_selector was provided and will not be used",t)},get mask_input_options(){return e.mask_input_options},set mask_input_options(t){t&&"object"==typeof t?e.mask_input_options={...t,password:!0}:(0,l.Z)("An invalid session_replay.mask_input_option was provided and will not be used",t)}},spa:{enabled:!0,harvestTimeSeconds:10,autoStart:!0}}},g={},p="All configuration objects require an agent identifier!";function h(e){if(!e)throw new Error(p);if(!g[e])throw new Error("Configuration for ".concat(e," was never set"));return g[e]}function v(e,t){if(!e)throw new Error(p);g[e]=(0,i.D)(t,f());const n=(0,r.ek)(e);n&&(n.init=g[e])}function m(e,t){if(!e)throw new Error(p);var n=h(e);if(n){for(var r=t.split("."),i=0;i<r.length-1;i++)if("object"!=typeof(n=n[r[i]]))return;n=n[r[r.length-1]]}return n}const b={accountID:void 0,trustKey:void 0,agentID:void 0,licenseKey:void 0,applicationID:void 0,xpid:void 0},y={};function w(e){if(!e)throw new Error("All loader-config objects require an agent identifier!");if(!y[e])throw new Error("LoaderConfig for ".concat(e," was never set"));return y[e]}function A(e,t){if(!e)throw new Error("All loader-config objects require an agent identifier!");y[e]=(0,i.D)(t,b);const n=(0,r.ek)(e);n&&(n.loader_config=y[e])}const _=(0,r.mF)().o;var x=n(385),D=n(6818);const k={buildEnv:D.Re,customTransaction:void 0,disabled:!1,distMethod:D.gF,isolatedBacklog:!1,loaderType:void 0,maxBytes:3e4,offset:Math.floor(x._A?.performance?.timeOrigin||x._A?.performance?.timing?.navigationStart||Date.now()),onerror:void 0,origin:""+x._A.location,ptid:void 0,releaseIds:{},session:void 0,xhrWrappable:"function"==typeof x._A.XMLHttpRequest?.prototype?.addEventListener,version:D.q4,denyList:void 0},E={};function j(e){if(!e)throw new Error("All runtime objects require an agent identifier!");if(!E[e])throw new Error("Runtime for ".concat(e," was never set"));return E[e]}function T(e,t){if(!e)throw new Error("All runtime objects require an agent identifier!");E[e]=(0,i.D)(t,k);const n=(0,r.ek)(e);n&&(n.runtime=E[e])}function R(e){return function(e){try{const t=s(e);return!!t.licenseKey&&!!t.errorBeacon&&!!t.applicationID}catch(e){return!1}}(e)}},9567:(e,t,n)=>{"use strict";n.d(t,{D:()=>i});var r=n(50);function i(e,t){try{if(!e||"object"!=typeof e)return(0,r.Z)("Setting a Configurable requires an object as input");if(!t||"object"!=typeof t)return(0,r.Z)("Setting a Configurable requires a model to set its initial properties");const n=Object.create(Object.getPrototypeOf(t),Object.getOwnPropertyDescriptors(t)),a=0===Object.keys(n).length?e:n;for(let o in a)if(void 0!==e[o])try{Array.isArray(e[o])&&Array.isArray(t[o])?n[o]=Array.from(new Set([...e[o],...t[o]])):"object"==typeof e[o]&&"object"==typeof t[o]?n[o]=i(e[o],t[o]):n[o]=e[o]}catch(e){(0,r.Z)("An error occurred while setting a property of a Configurable",e)}return n}catch(e){(0,r.Z)("An error occured while setting a Configurable",e)}}},6818:(e,t,n)=>{"use strict";n.d(t,{Re:()=>i,gF:()=>a,q4:()=>r});const r="1.248.0",i="PROD",a="CDN"},385:(e,t,n)=>{"use strict";n.d(t,{Nk:()=>d,Tt:()=>s,_A:()=>a,cv:()=>l,iS:()=>o,il:()=>r,ux:()=>c,v6:()=>i,w1:()=>u});const r="undefined"!=typeof window&&!!window.document,i="undefined"!=typeof WorkerGlobalScope&&("undefined"!=typeof self&&self instanceof WorkerGlobalScope&&self.navigator instanceof WorkerNavigator||"undefined"!=typeof globalThis&&globalThis instanceof WorkerGlobalScope&&globalThis.navigator instanceof WorkerNavigator),a=r?window:"undefined"!=typeof WorkerGlobalScope&&("undefined"!=typeof self&&self instanceof WorkerGlobalScope&&self||"undefined"!=typeof globalThis&&globalThis instanceof WorkerGlobalScope&&globalThis),o=(a?.document?.readyState,Boolean("hidden"===a?.document?.visibilityState)),s=(a?.location,/iPad|iPhone|iPod/.test(a.navigator?.userAgent)),c=s&&"undefined"==typeof SharedWorker,u=((()=>{const e=a.navigator?.userAgent?.match(/Firefox[/\s](\d+\.\d+)/);Array.isArray(e)&&e.length>=2&&e[1]})(),Boolean(r&&window.document.documentMode)),d=!!a.navigator?.sendBeacon,l=Math.floor(a?.performance?.timeOrigin||a?.performance?.timing?.navigationStart||Date.now())},1117:(e,t,n)=>{"use strict";n.d(t,{w:()=>a});var r=n(50);const i={agentIdentifier:"",ee:void 0};class a{constructor(e){try{if("object"!=typeof e)return(0,r.Z)("shared context requires an object as input");this.sharedContext={},Object.assign(this.sharedContext,i),Object.entries(e).forEach((e=>{let[t,n]=e;Object.keys(i).includes(t)&&(this.sharedContext[t]=n)}))}catch(e){(0,r.Z)("An error occured while setting SharedContext",e)}}}},8e3:(e,t,n)=>{"use strict";n.d(t,{L:()=>d,R:()=>c});var r=n(8325),i=n(1284),a=n(4322),o=n(3325);const s={};function c(e,t){const n={staged:!1,priority:o.p[t]||0};u(e),s[e].get(t)||s[e].set(t,n)}function u(e){e&&(s[e]||(s[e]=new Map))}function d(){let e=arguments.length>0&&void 0!==arguments[0]?arguments[0]:"",t=arguments.length>1&&void 0!==arguments[1]?arguments[1]:"feature";if(u(e),!e||!s[e].get(t))return o(t);s[e].get(t).staged=!0;const n=[...s[e]];function o(t){const n=e?r.ee.get(e):r.ee,o=a.X.handlers;if(n.backlog&&o){var s=n.backlog[t],c=o[t];if(c){for(var u=0;s&&u<s.length;++u)l(s[u],c);(0,i.D)(c,(function(e,t){(0,i.D)(t,(function(t,n){n[0].on(e,n[1])}))}))}delete o[t],n.backlog[t]=null,n.emit("drain-"+t,[])}}n.every((e=>{let[t,n]=e;return n.staged}))&&(n.sort(((e,t)=>e[1].priority-t[1].priority)),n.forEach((t=>{let[n]=t;s[e].delete(n),o(n)})))}function l(e,t){var n=e[1];(0,i.D)(t[n],(function(t,n){var r=e[0];if(n[0]===r){var i=n[1],a=e[3],o=e[2];i.apply(a,o)}}))}},8325:(e,t,n)=>{"use strict";n.d(t,{A:()=>c,ee:()=>u});var r=n(8632),i=n(2210),a=n(234);class o{constructor(e){this.contextId=e}}var s=n(3117);const c="nr@context:".concat(s.a),u=function e(t,n){var r={},s={},d={},f=!1;try{f=16===n.length&&(0,a.OP)(n).isolatedBacklog}catch(e){}var g={on:h,addEventListener:h,removeEventListener:function(e,t){var n=r[e];if(!n)return;for(var i=0;i<n.length;i++)n[i]===t&&n.splice(i,1)},emit:function(e,n,r,i,a){!1!==a&&(a=!0);if(u.aborted&&!i)return;t&&a&&t.emit(e,n,r);for(var o=p(r),c=v(e),d=c.length,l=0;l<d;l++)c[l].apply(o,n);var f=b()[s[e]];f&&f.push([g,e,n,o]);return o},get:m,listeners:v,context:p,buffer:function(e,t){const n=b();if(t=t||"feature",g.aborted)return;Object.entries(e||{}).forEach((e=>{let[r,i]=e;s[i]=t,t in n||(n[t]=[])}))},abort:l,aborted:!1,isBuffering:function(e){return!!b()[s[e]]},debugId:n,backlog:f?{}:t&&"object"==typeof t.backlog?t.backlog:{}};return g;function p(e){return e&&e instanceof o?e:e?(0,i.X)(e,c,(()=>new o(c))):new o(c)}function h(e,t){r[e]=v(e).concat(t)}function v(e){return r[e]||[]}function m(t){return d[t]=d[t]||e(g,t)}function b(){return g.backlog}}(void 0,"globalEE"),d=(0,r.fP)();function l(){u.aborted=!0,u.backlog={}}d.ee||(d.ee=u)},5546:(e,t,n)=>{"use strict";n.d(t,{E:()=>r,p:()=>i});var r=n(8325).ee.get("handle");function i(e,t,n,i,a){a?(a.buffer([e],i),a.emit(e,t,n)):(r.buffer([e],i),r.emit(e,t,n))}},4322:(e,t,n)=>{"use strict";n.d(t,{X:()=>a});var r=n(5546);a.on=o;var i=a.handlers={};function a(e,t,n,a){o(a||r.E,i,e,t,n)}function o(e,t,n,i,a){a||(a="feature"),e||(e=r.E);var o=t[a]=t[a]||{};(o[n]=o[n]||[]).push([e,i])}},3239:(e,t,n)=>{"use strict";n.d(t,{bP:()=>s,iz:()=>c,m$:()=>o});var r=n(385);let i=!1,a=!1;try{const e={get passive(){return i=!0,!1},get signal(){return a=!0,!1}};r._A.addEventListener("test",null,e),r._A.removeEventListener("test",null,e)}catch(e){}function o(e,t){return i||a?{capture:!!e,passive:i,signal:t}:!!e}function s(e,t){let n=arguments.length>2&&void 0!==arguments[2]&&arguments[2],r=arguments.length>3?arguments[3]:void 0;window.addEventListener(e,t,o(n,r))}function c(e,t){let n=arguments.length>2&&void 0!==arguments[2]&&arguments[2],r=arguments.length>3?arguments[3]:void 0;document.addEventListener(e,t,o(n,r))}},3117:(e,t,n)=>{"use strict";n.d(t,{a:()=>r});const r=(0,n(4402).Rl)()},4402:(e,t,n)=>{"use strict";n.d(t,{Rl:()=>o,ky:()=>s});var r=n(385);const i="xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx";function a(e,t){return e?15&e[t]:16*Math.random()|0}function o(){const e=r._A?.crypto||r._A?.msCrypto;let t,n=0;return e&&e.getRandomValues&&(t=e.getRandomValues(new Uint8Array(31))),i.split("").map((e=>"x"===e?a(t,++n).toString(16):"y"===e?(3&a()|8).toString(16):e)).join("")}function s(e){const t=r._A?.crypto||r._A?.msCrypto;let n,i=0;t&&t.getRandomValues&&(n=t.getRandomValues(new Uint8Array(31)));const o=[];for(var s=0;s<e;s++)o.push(a(n,++i).toString(16));return o.join("")}},7056:(e,t,n)=>{"use strict";n.d(t,{Bq:()=>r,Hb:()=>a,oD:()=>i});const r="NRBA",i=144e5,a=18e5},7894:(e,t,n)=>{"use strict";function r(){return Math.round(performance.now())}n.d(t,{z:()=>r})},50:(e,t,n)=>{"use strict";function r(e,t){"function"==typeof console.warn&&(console.warn("New Relic: ".concat(e)),t&&console.warn(t))}n.d(t,{Z:()=>r})},2825:(e,t,n)=>{"use strict";n.d(t,{N:()=>d,T:()=>l});var r=n(8325),i=n(5546),a=n(3325),o=n(385);const s="newrelic";const c={stn:[a.D.sessionTrace],err:[a.D.jserrors,a.D.metrics],ins:[a.D.pageAction],spa:[a.D.spa],sr:[a.D.sessionReplay,a.D.sessionTrace]},u=new Set;function d(e,t){const n=r.ee.get(t);e&&"object"==typeof e&&(u.has(t)||(Object.entries(e).forEach((e=>{let[t,r]=e;c[t]?c[t].forEach((e=>{r?(0,i.p)("feat-"+t,[],void 0,e,n):(0,i.p)("block-"+t,[],void 0,e,n),(0,i.p)("rumresp-"+t,[Boolean(r)],void 0,e,n)})):r&&(0,i.p)("feat-"+t,[],void 0,void 0,n),l[t]=Boolean(r)})),Object.keys(c).forEach((e=>{void 0===l[e]&&(c[e]?.forEach((t=>(0,i.p)("rumresp-"+e,[!1],void 0,t,n))),l[e]=!1)})),u.add(t),function(){let e=arguments.length>0&&void 0!==arguments[0]?arguments[0]:{};try{o._A.dispatchEvent(new CustomEvent(s,{detail:e}))}catch(e){}}({loaded:!0})))}const l={}},2210:(e,t,n)=>{"use strict";n.d(t,{X:()=>i});var r=Object.prototype.hasOwnProperty;function i(e,t,n){if(r.call(e,t))return e[t];var i=n();if(Object.defineProperty&&Object.keys)try{return Object.defineProperty(e,t,{value:i,writable:!0,enumerable:!1}),i}catch(e){}return e[t]=i,i}},1284:(e,t,n)=>{"use strict";n.d(t,{D:()=>r});const r=(e,t)=>Object.entries(e||{}).map((e=>{let[n,r]=e;return t(n,r)}))},4351:(e,t,n)=>{"use strict";n.d(t,{P:()=>a});var r=n(8325);const i=()=>{const e=new WeakSet;return(t,n)=>{if("object"==typeof n&&null!==n){if(e.has(n))return;e.add(n)}return n}};function a(e){try{return JSON.stringify(e,i())}catch(e){try{r.ee.emit("internal-error",[e])}catch(e){}}}},3960:(e,t,n)=>{"use strict";n.d(t,{KB:()=>o,b2:()=>a});var r=n(3239);function i(){return"undefined"==typeof document||"complete"===document.readyState}function a(e,t){if(i())return e();(0,r.bP)("load",e,t)}function o(e){if(i())return e();(0,r.iz)("DOMContentLoaded",e)}},8632:(e,t,n)=>{"use strict";n.d(t,{EZ:()=>d,ce:()=>a,ek:()=>u,fP:()=>o,gG:()=>l,h5:()=>c,mF:()=>s});var r=n(7894),i=n(385);const a={beacon:"bam.nr-data.net",errorBeacon:"bam.nr-data.net"};function o(){return i._A.NREUM||(i._A.NREUM={}),void 0===i._A.newrelic&&(i._A.newrelic=i._A.NREUM),i._A.NREUM}function s(){let e=o();return e.o||(e.o={ST:i._A.setTimeout,SI:i._A.setImmediate,CT:i._A.clearTimeout,XHR:i._A.XMLHttpRequest,REQ:i._A.Request,EV:i._A.Event,PR:i._A.Promise,MO:i._A.MutationObserver,FETCH:i._A.fetch}),e}function c(e,t){let n=o();n.initializedAgents??={},t.initializedAt={ms:(0,r.z)(),date:new Date},n.initializedAgents[e]=t}function u(e){let t=o();return t.initializedAgents?.[e]}function d(e,t){o()[e]=t}function l(){return function(){let e=o();const t=e.info||{};e.info={beacon:a.beacon,errorBeacon:a.errorBeacon,...t}}(),function(){let e=o();const t=e.init||{};e.init={...t}}(),s(),function(){let e=o();const t=e.loader_config||{};e.loader_config={...t}}(),o()}},7956:(e,t,n)=>{"use strict";n.d(t,{N:()=>i});var r=n(3239);function i(e){let t=arguments.length>1&&void 0!==arguments[1]&&arguments[1],n=arguments.length>2?arguments[2]:void 0,i=arguments.length>3?arguments[3]:void 0;(0,r.iz)("visibilitychange",(function(){if(t)return void("hidden"===document.visibilityState&&e());e(document.visibilityState)}),n,i)}},3081:(e,t,n)=>{"use strict";n.d(t,{gF:()=>a,mY:()=>i,t9:()=>r,vz:()=>s,xS:()=>o});const r=n(3325).D.metrics,i="sm",a="cm",o="storeSupportabilityMetrics",s="storeEventMetrics"},7633:(e,t,n)=>{"use strict";n.d(t,{t:()=>r});const r=n(3325).D.pageViewEvent},9251:(e,t,n)=>{"use strict";n.d(t,{t:()=>r});const r=n(3325).D.pageViewTiming},5938:(e,t,n)=>{"use strict";n.d(t,{W:()=>i});var r=n(8325);class i{constructor(e,t,n){this.agentIdentifier=e,this.aggregator=t,this.ee=r.ee.get(e),this.featureName=n,this.blocked=!1}}},7530:(e,t,n)=>{"use strict";n.d(t,{j:()=>b});var r=n(3325),i=n(234),a=n(5546),o=n(8325),s=n(7894),c=n(8e3),u=n(3960),d=n(385),l=n(50),f=n(3081),g=n(8632);function p(){const e=(0,g.gG)();["setErrorHandler","finished","addToTrace","addRelease","addPageAction","setCurrentRouteName","setPageViewName","setCustomAttribute","interaction","noticeError","setUserId","setApplicationVersion","start","recordReplay","pauseReplay"].forEach((t=>{e[t]=function(){for(var n=arguments.length,r=new Array(n),i=0;i<n;i++)r[i]=arguments[i];return function(t){for(var n=arguments.length,r=new Array(n>1?n-1:0),i=1;i<n;i++)r[i-1]=arguments[i];let a=[];return Object.values(e.initializedAgents).forEach((e=>{e.exposed&&e.api[t]&&a.push(e.api[t](...r))})),a.length>1?a:a[0]}(t,...r)}}))}var h=n(2825);const v=e=>{const t=e.startsWith("http");e+="/",n.p=t?e:"https://"+e};let m=!1;function b(e){let t=arguments.length>1&&void 0!==arguments[1]?arguments[1]:{},b=arguments.length>2?arguments[2]:void 0,y=arguments.length>3?arguments[3]:void 0,{init:w,info:A,loader_config:_,runtime:x={loaderType:b},exposed:D=!0}=t;const k=(0,g.gG)();A||(w=k.init,A=k.info,_=k.loader_config),(0,i.Dg)(e.agentIdentifier,w||{}),(0,i.GE)(e.agentIdentifier,_||{}),A.jsAttributes??={},d.v6&&(A.jsAttributes.isWorker=!0),(0,i.CX)(e.agentIdentifier,A);const E=(0,i.P_)(e.agentIdentifier),j=[A.beacon,A.errorBeacon];m||(E.proxy.assets&&(v(E.proxy.assets),j.push(E.proxy.assets)),E.proxy.beacon&&j.push(E.proxy.beacon),p(),(0,g.EZ)("activatedFeatures",h.T)),x.denyList=[...E.ajax.deny_list||[],...E.ajax.block_internal?j:[]],(0,i.sU)(e.agentIdentifier,x),void 0===e.api&&(e.api=function(e,t){t||(0,c.R)(e,"api");const g={};var p=o.ee.get(e),h=p.get("tracer"),v="api-",m=v+"ixn-";function b(t,n,r,a){const o=(0,i.C5)(e);return null===n?delete o.jsAttributes[t]:(0,i.CX)(e,{...o,jsAttributes:{...o.jsAttributes,[t]:n}}),A(v,r,!0,a||null===n?"session":void 0)(t,n)}function y(){}["setErrorHandler","finished","addToTrace","addRelease"].forEach((e=>{g[e]=A(v,e,!0,"api")})),g.addPageAction=A(v,"addPageAction",!0,r.D.pageAction),g.setCurrentRouteName=A(v,"routeName",!0,r.D.spa),g.setPageViewName=function(t,n){if("string"==typeof t)return"/"!==t.charAt(0)&&(t="/"+t),(0,i.OP)(e).customTransaction=(n||"https://web.archive.org/web/20231209224628/http://custom.transaction")+t,A(v,"setPageViewName",!0)()},g.setCustomAttribute=function(e,t){let n=arguments.length>2&&void 0!==arguments[2]&&arguments[2];if("string"==typeof e){if(["string","number","boolean"].includes(typeof t)||null===t)return b(e,t,"setCustomAttribute",n);(0,l.Z)("Failed to execute setCustomAttribute.\nNon-null value must be a string, number or boolean type, but a type of <".concat(typeof t,"> was provided."))}else(0,l.Z)("Failed to execute setCustomAttribute.\nName must be a string type, but a type of <".concat(typeof e,"> was provided."))},g.setUserId=function(e){if("string"==typeof e||null===e)return b("enduser.id",e,"setUserId",!0);(0,l.Z)("Failed to execute setUserId.\nNon-null value must be a string type, but a type of <".concat(typeof e,"> was provided."))},g.setApplicationVersion=function(e){if("string"==typeof e||null===e)return b("application.version",e,"setApplicationVersion",!1);(0,l.Z)("Failed to execute setApplicationVersion. Expected <String | null>, but got <".concat(typeof e,">."))},g.start=e=>{try{const t=e?"defined":"undefined";(0,a.p)(f.xS,["API/start/".concat(t,"/called")],void 0,r.D.metrics,p);const n=Object.values(r.D);if(void 0===e)e=n;else{if((e=Array.isArray(e)&&e.length?e:[e]).some((e=>!n.includes(e))))return(0,l.Z)("Invalid feature name supplied. Acceptable feature names are: ".concat(n));e.includes(r.D.pageViewEvent)||e.push(r.D.pageViewEvent)}e.forEach((e=>{p.emit("".concat(e,"-opt-in"))}))}catch(e){(0,l.Z)("An unexpected issue occurred",e)}},g.recordReplay=function(){(0,a.p)(f.xS,["API/recordReplay/called"],void 0,r.D.metrics,p),(0,a.p)("recordReplay",[],void 0,r.D.sessionReplay,p)},g.pauseReplay=function(){(0,a.p)(f.xS,["API/pauseReplay/called"],void 0,r.D.metrics,p),(0,a.p)("pauseReplay",[],void 0,r.D.sessionReplay,p)},g.interaction=function(){return(new y).get()};var w=y.prototype={createTracer:function(e,t){var n={},i=this,o="function"==typeof t;return(0,a.p)(f.xS,["API/createTracer/called"],void 0,r.D.metrics,p),(0,a.p)(m+"tracer",[(0,s.z)(),e,n],i,r.D.spa,p),function(){if(h.emit((o?"":"no-")+"fn-start",[(0,s.z)(),i,o],n),o)try{return t.apply(this,arguments)}catch(e){throw h.emit("fn-err",[arguments,this,e],n),e}finally{h.emit("fn-end",[(0,s.z)()],n)}}}};function A(e,t,n,i){return function(){return(0,a.p)(f.xS,["API/"+t+"/called"],void 0,r.D.metrics,p),i&&(0,a.p)(e+t,[(0,s.z)(),...arguments],n?null:this,i,p),n?void 0:this}}function _(){n.e(75).then(n.bind(n,7438)).then((t=>{let{setAPI:n}=t;n(e),(0,c.L)(e,"api")})).catch((()=>(0,l.Z)("Downloading runtime APIs failed...")))}return["actionText","setName","setAttribute","save","ignore","onEnd","getContext","end","get"].forEach((e=>{w[e]=A(m,e,void 0,r.D.spa)})),g.noticeError=function(e,t){"string"==typeof e&&(e=new Error(e)),(0,a.p)(f.xS,["API/noticeError/called"],void 0,r.D.metrics,p),(0,a.p)("err",[e,(0,s.z)(),!1,t],void 0,r.D.jserrors,p)},d.il?(0,u.b2)((()=>_()),!0):_(),g}(e.agentIdentifier,y)),void 0===e.exposed&&(e.exposed=D),m=!0}},1926:(e,t,n)=>{n.nc=(()=>{try{return document?.currentScript?.nonce}catch(e){}return""})()},3325:(e,t,n)=>{"use strict";n.d(t,{D:()=>r,p:()=>i});const r={ajax:"ajax",jserrors:"jserrors",metrics:"metrics",pageAction:"page_action",pageViewEvent:"page_view_event",pageViewTiming:"page_view_timing",sessionReplay:"session_replay",sessionTrace:"session_trace",spa:"spa"},i={[r.pageViewEvent]:1,[r.pageViewTiming]:2,[r.metrics]:3,[r.jserrors]:4,[r.ajax]:5,[r.sessionTrace]:6,[r.pageAction]:7,[r.spa]:8,[r.sessionReplay]:9}}},r={};function i(e){var t=r[e];if(void 0!==t)return t.exports;var a=r[e]={exports:{}};return n[e](a,a.exports,i),a.exports}i.m=n,i.d=(e,t)=>{for(var n in t)i.o(t,n)&&!i.o(e,n)&&Object.defineProperty(e,n,{enumerable:!0,get:t[n]})},i.f={},i.e=e=>Promise.all(Object.keys(i.f).reduce(((t,n)=>(i.f[n](e,t),t)),[])),i.u=e=>"nr-rum-1.248.0.min.js",i.o=(e,t)=>Object.prototype.hasOwnProperty.call(e,t),e={},t="NRBA-1.248.0.PROD:",i.l=(n,r,a,o)=>{if(e[n])e[n].push(r);else{var s,c;if(void 0!==a)for(var u=document.getElementsByTagName("script"),d=0;d<u.length;d++){var l=u[d];if(l.getAttribute("src")==n||l.getAttribute("data-webpack")==t+a){s=l;break}}s||(c=!0,(s=document.createElement("script")).charset="utf-8",s.timeout=120,i.nc&&s.setAttribute("nonce",i.nc),s.setAttribute("data-webpack",t+a),s.src=n,0!==s.src.indexOf(window.location.origin+"/")&&(s.crossOrigin="anonymous"),s.integrity=i.sriHashes[o],s.crossOrigin="anonymous"),e[n]=[r];var f=(t,r)=>{s.onerror=s.onload=null,clearTimeout(g);var i=e[n];if(delete e[n],s.parentNode&&s.parentNode.removeChild(s),i&&i.forEach((e=>e(r))),t)return t(r)},g=setTimeout(f.bind(null,void 0,{type:"timeout",target:s}),12e4);s.onerror=f.bind(null,s.onerror),s.onload=f.bind(null,s.onload),c&&document.head.appendChild(s)}},i.r=e=>{"undefined"!=typeof Symbol&&Symbol.toStringTag&&Object.defineProperty(e,Symbol.toStringTag,{value:"Module"}),Object.defineProperty(e,"__esModule",{value:!0})},i.p="https://web.archive.org/web/20231209224628/https://js-agent.newrelic.com/",i.sriHashes={75:"sha512-5mWtMwj7hrXT5aUkfvBtjH6FJXsR+zdeMBfc721nzrOx36xa23yTrCB1VVOAQa+zIioAbWPW4m7UsPp7hW1WPw=="},(()=>{var e={50:0,832:0};i.f.j=(t,n)=>{var r=i.o(e,t)?e[t]:void 0;if(0!==r)if(r)n.push(r[2]);else{var a=new Promise(((n,i)=>r=e[t]=[n,i]));n.push(r[2]=a);var o=i.p+i.u(t),s=new Error;i.l(o,(n=>{if(i.o(e,t)&&(0!==(r=e[t])&&(e[t]=void 0),r)){var a=n&&("load"===n.type?"missing":n.type),o=n&&n.target&&n.target.src;s.message="Loading chunk "+t+" failed.\n("+a+": "+o+")",s.name="ChunkLoadError",s.type=a,s.request=o,r[1](s)}}),"chunk-"+t,t)}};var t=(t,n)=>{var r,a,[o,s,c]=n,u=0;if(o.some((t=>0!==e[t]))){for(r in s)i.o(s,r)&&(i.m[r]=s[r]);if(c)c(i)}for(t&&t(n);u<o.length;u++)a=o[u],i.o(e,a)&&e[a]&&e[a][0](),e[a]=0},n=self["webpackChunk:NRBA-1.248.0.PROD"]=self["webpackChunk:NRBA-1.248.0.PROD"]||[];n.forEach(t.bind(null,0)),n.push=t.bind(null,n.push.bind(n))})(),(()=>{"use strict";i(1926);var e=i(50);class t{addPageAction(t,n){(0,e.Z)("Call to agent api addPageAction failed. The page action feature is not currently initialized.")}setPageViewName(t,n){(0,e.Z)("Call to agent api setPageViewName failed. The page view feature is not currently initialized.")}setCustomAttribute(t,n,r){(0,e.Z)("Call to agent api setCustomAttribute failed. The js errors feature is not currently initialized.")}noticeError(t,n){(0,e.Z)("Call to agent api noticeError failed. The js errors feature is not currently initialized.")}setUserId(t){(0,e.Z)("Call to agent api setUserId failed. The js errors feature is not currently initialized.")}setApplicationVersion(t){(0,e.Z)("Call to agent api setApplicationVersion failed. The agent is not currently initialized.")}setErrorHandler(t){(0,e.Z)("Call to agent api setErrorHandler failed. The js errors feature is not currently initialized.")}finished(t){(0,e.Z)("Call to agent api finished failed. The page action feature is not currently initialized.")}addRelease(t,n){(0,e.Z)("Call to agent api addRelease failed. The js errors feature is not currently initialized.")}start(t){(0,e.Z)("Call to agent api addRelease failed. The agent is not currently initialized.")}recordReplay(){(0,e.Z)("Call to agent api recordReplay failed. The agent is not currently initialized.")}pauseReplay(){(0,e.Z)("Call to agent api pauseReplay failed. The agent is not currently initialized.")}}var n=i(3325),r=i(234);const a=Object.values(n.D);function o(e){const t={};return a.forEach((n=>{t[n]=function(e,t){return!1!==(0,r.Mt)(t,"".concat(e,".enabled"))}(n,e)})),t}var s=i(7530);var c=i(8e3),u=i(5938),d=i(3960),l=i(385);class f extends u.W{constructor(e,t,n){let i=!(arguments.length>3&&void 0!==arguments[3])||arguments[3];super(e,t,n),this.auto=i,this.abortHandler=void 0,this.featAggregate=void 0,this.onAggregateImported=void 0,!1===(0,r.Mt)(this.agentIdentifier,"".concat(this.featureName,".autoStart"))&&(this.auto=!1),this.auto&&(0,c.R)(e,n)}importAggregator(){let t=arguments.length>0&&void 0!==arguments[0]?arguments[0]:{};if(this.featAggregate)return;if(!this.auto)return void this.ee.on("".concat(this.featureName,"-opt-in"),(()=>{(0,c.R)(this.agentIdentifier,this.featureName),this.auto=!0,this.importAggregator()}));const n=l.il&&!0===(0,r.Mt)(this.agentIdentifier,"privacy.cookies_enabled");let a;this.onAggregateImported=new Promise((e=>{a=e}));const o=async()=>{let r;try{if(n){const{setupAgentSession:e}=await i.e(75).then(i.bind(i,3228));r=e(this.agentIdentifier)}}catch(t){(0,e.Z)("A problem occurred when starting up session manager. This page will not start or extend any session.",t)}try{if(!this.shouldImportAgg(this.featureName,r))return(0,c.L)(this.agentIdentifier,this.featureName),void a(!1);const{lazyFeatureLoader:e}=await i.e(75).then(i.bind(i,8582)),{Aggregate:n}=await e(this.featureName,"aggregate");this.featAggregate=new n(this.agentIdentifier,this.aggregator,t),a(!0)}catch(t){(0,e.Z)("Downloading and initializing ".concat(this.featureName," failed..."),t),this.abortHandler?.(),(0,c.L)(this.agentIdentifier,this.featureName),a(!1)}};l.il?(0,d.b2)((()=>o()),!0):o()}shouldImportAgg(e,t){return e!==n.D.sessionReplay||!!r.Yu.MO&&(!1!==(0,r.Mt)(this.agentIdentifier,"session_trace.enabled")&&(!!t?.isNew||!!t?.state.sessionReplayMode))}}var g=i(7633);class p extends f{static featureName=g.t;constructor(e,t){let n=!(arguments.length>2&&void 0!==arguments[2])||arguments[2];super(e,t,g.t,n),this.importAggregator()}}var h=i(1117),v=i(1284);class m extends h.w{constructor(e){super(e),this.aggregatedData={}}store(e,t,n,r,i){var a=this.getBucket(e,t,n,i);return a.metrics=function(e,t){t||(t={count:0});return t.count+=1,(0,v.D)(e,(function(e,n){t[e]=b(n,t[e])})),t}(r,a.metrics),a}merge(e,t,n,r,i){var a=this.getBucket(e,t,r,i);if(a.metrics){var o=a.metrics;o.count+=n.count,(0,v.D)(n,(function(e,t){if("count"!==e){var r=o[e],i=n[e];i&&!i.c?o[e]=b(i.t,r):o[e]=function(e,t){if(!t)return e;t.c||(t=y(t.t));return t.min=Math.min(e.min,t.min),t.max=Math.max(e.max,t.max),t.t+=e.t,t.sos+=e.sos,t.c+=e.c,t}(i,o[e])}}))}else a.metrics=n}storeMetric(e,t,n,r){var i=this.getBucket(e,t,n);return i.stats=b(r,i.stats),i}getBucket(e,t,n,r){this.aggregatedData[e]||(this.aggregatedData[e]={});var i=this.aggregatedData[e][t];return i||(i=this.aggregatedData[e][t]={params:n||{}},r&&(i.custom=r)),i}get(e,t){return t?this.aggregatedData[e]&&this.aggregatedData[e][t]:this.aggregatedData[e]}take(e){for(var t={},n="",r=!1,i=0;i<e.length;i++)t[n=e[i]]=w(this.aggregatedData[n]),t[n].length&&(r=!0),delete this.aggregatedData[n];return r?t:null}}function b(e,t){return null==e?function(e){e?e.c++:e={c:1};return e}(t):t?(t.c||(t=y(t.t)),t.c+=1,t.t+=e,t.sos+=e*e,e>t.max&&(t.max=e),e<t.min&&(t.min=e),t):{t:e}}function y(e){return{t:e,min:e,max:e,sos:e*e,c:1}}function w(e){return"object"!=typeof e?[]:(0,v.D)(e,A)}function A(e,t){return t}var _=i(8632),x=i(4402),D=i(4351);var k=i(5546),E=i(7956),j=i(3239),T=i(7894),R=i(9251);class S extends f{static featureName=R.t;constructor(e,t){let n=!(arguments.length>2&&void 0!==arguments[2])||arguments[2];super(e,t,R.t,n),l.il&&((0,E.N)((()=>(0,k.p)("docHidden",[(0,T.z)()],void 0,R.t,this.ee)),!0),(0,j.bP)("pagehide",(()=>(0,k.p)("winPagehide",[(0,T.z)()],void 0,R.t,this.ee))),this.importAggregator())}}var I=i(3081);class C extends f{static featureName=I.t9;constructor(e,t){let n=!(arguments.length>2&&void 0!==arguments[2])||arguments[2];super(e,t,I.t9,n),this.importAggregator()}}new class extends t{constructor(t){let n=arguments.length>1&&void 0!==arguments[1]?arguments[1]:(0,x.ky)(16);super(),l._A?(this.agentIdentifier=n,this.sharedAggregator=new m({agentIdentifier:this.agentIdentifier}),this.features={},(0,_.h5)(n,this),this.desiredFeatures=new Set(t.features||[]),this.desiredFeatures.add(p),(0,s.j)(this,t,t.loaderType||"agent"),this.run()):(0,e.Z)("Failed to initial the agent. Could not determine the runtime environment.")}get config(){return{info:(0,r.C5)(this.agentIdentifier),init:(0,r.P_)(this.agentIdentifier),loader_config:(0,r.DL)(this.agentIdentifier),runtime:(0,r.OP)(this.agentIdentifier)}}run(){try{const t=o(this.agentIdentifier),r=[...this.desiredFeatures];r.sort(((e,t)=>n.p[e.featureName]-n.p[t.featureName])),r.forEach((r=>{if(t[r.featureName]||r.featureName===n.D.pageViewEvent){const i=function(e){switch(e){case n.D.ajax:return[n.D.jserrors];case n.D.sessionTrace:return[n.D.ajax,n.D.pageViewEvent];case n.D.sessionReplay:return[n.D.sessionTrace];case n.D.pageViewTiming:return[n.D.pageViewEvent];default:return[]}}(r.featureName);i.every((e=>t[e]))||(0,e.Z)("".concat(r.featureName," is enabled but one or more dependent features has been disabled (").concat((0,D.P)(i),"). This may cause unintended consequences or missing data...")),this.features[r.featureName]=new r(this.agentIdentifier,this.sharedAggregator)}}))}catch(t){(0,e.Z)("Failed to initialize all enabled instrument classes (agent aborted) -",t);for(const e in this.features)this.features[e].abortHandler?.();const n=(0,_.fP)();return delete n.initializedAgents[this.agentIdentifier]?.api,delete n.initializedAgents[this.agentIdentifier]?.features,delete this.sharedAggregator,n.ee?.abort(),delete n.ee?.get(this.agentIdentifier),!1}}addToTrace(t){(0,e.Z)("Call to agent api addToTrace failed. The session trace feature is not currently initialized.")}setCurrentRouteName(t){(0,e.Z)("Call to agent api setCurrentRouteName failed. The spa feature is not currently initialized.")}interaction(){(0,e.Z)("Call to agent api interaction failed. The spa feature is not currently initialized.")}}({features:[p,S,C],loaderType:"lite"})})()})();</script> <noscript><style>form.antibot * :not(.antibot-message) { display: none !important; }</style> </noscript><script async src="https://web.archive.org/web/20231209224628js_/https://www.googletagmanager.com/gtag/js?id=G-HEQ0YF2VYL"></script> <script>window.dataLayer = window.dataLayer || [];function gtag(){dataLayer.push(arguments)};gtag("js", new Date());gtag("set", "developer_id.dMDhkMT", true);gtag('set', {'cookie_flags': 'SameSite=None;Secure', 'cookie_domain': 'www.nist.gov'});gtag("config", "G-HEQ0YF2VYL", {"groups":"default","page_placeholder":"PLACEHOLDER_page_location","link_attribution":true,"allow_ad_personalization_signals":false});gtag("event", "custom", {"node_title":"Time Realization and Distribution Group","node_id":"411331","content_type":"Laboratory\/Organizational Unit"});</script> <meta name="description" content="The Time Realization and Distribution group distributes standard time and frequency signals generated by the Coordinated Universal Time scale, UTC(NIST), maintained at the NIST laboratories in Boulder, Colorado. UTC(NIST) is the U. S."/> <link rel="canonical" href="https://web.archive.org/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-services"/> <link rel="shortlink" href="https://web.archive.org/web/20231209224628/https://www.nist.gov/node/411331"/> <meta name="citation_title" content="Time Realization and Distribution Group | NIST"/> <meta property="og:site_name" content="NIST"/> <meta property="og:type" content="Article"/> <meta property="og:url" content="https://web.archive.org/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-services"/> <meta property="og:title" content="Time Realization and Distribution Group"/> <meta property="og:description" content="The Time Realization and Distribution group distributes standard time and frequency signals generated by the Coordinated Universal Time scale, UTC(NIST), maintained at the NIST laboratories in Boulder, Colorado. UTC(NIST) is the U. S."/> <meta property="article:published_time" content="2009-07-02T10:09-04:00"/> <meta property="article:modified_time" content="2023-11-14T16:10-05:00"/> <meta name="dcterms.title" content="Time Realization and Distribution Group"/> <meta name="dcterms.description" content="The Time Realization and Distribution group distributes standard time and frequency signals generated by the Coordinated Universal Time scale, UTC(NIST), maintained at the NIST laboratories in Boulder, Colorado. UTC(NIST) is the U. S."/> <meta name="dcterms.date" content="2009-07-02T10:09-04:00"/> <meta name="dcterms.type" content="text"/> <meta name="dcterms.format" content="text/html"/> <meta name="dcterms.identifier" content="https://www.nist.gov/pml/time-and-frequency-division/time-services"/> <meta name="dcterms.source" content="NIST"/> <meta name="dcterms.created" content="2009-07-02T10:09-04:00"/> <meta name="dcterms.modified" content="2023-11-14T16:10-05:00"/> <meta name="twitter:card" content="summary_large_image"/> <meta name="twitter:description" content="The Time Realization and Distribution group distributes standard time and frequency signals generated by the Coordinated Universal Time scale, UTC(NIST), maintained at the NIST laboratories in Boulder, Colorado. UTC(NIST) is the U. S."/> <meta name="twitter:site" content="NIST"/> <meta name="twitter:title" content="Time Realization and Distribution Group"/> <meta name="google-site-verification" content="QMu0ODkER3rN5hLcMLqNVf7e3bkjYsNLTuhqfH48jCA"/> <meta name="Generator" content="Drupal 10 (https://www.drupal.org)"/> <meta name="MobileOptimized" content="width"/> <meta name="HandheldFriendly" content="true"/> <meta name="viewport" content="width=device-width, initial-scale=1.0"/> <meta name="nist_search_modified" class="elastic" content="2023-11-14T16:10:00-05:00"/> <script type="application/ld+json">{ "@context": "https://web.archive.org/web/20231209224628/https://schema.org", "@graph": [ { "@type": "Article", "headline": "Time Realization and Distribution Group | NIST", "description": "The Time Realization and Distribution group distributes standard time and frequency signals generated by the Coordinated Universal Time scale, UTC(NIST), maintained at the NIST laboratories in Boulder, Colorado. UTC(NIST) is the U. S.", "datePublished": "2009-07-02T10:09-04:00", "dateModified": "2023-11-14T16:10-05:00" } ] }</script> <meta name="nist_search_bundle" class="elastic" content="laboratory_organizational_unit"/> <link rel="icon" href="/web/20231209224628im_/https://www.nist.gov/themes/custom/nist_www/favicon.ico" type="image/vnd.microsoft.icon"/> <title>Time Realization and Distribution Group | NIST</title> <link rel="stylesheet" media="all" href="/web/20231209224628cs_/https://www.nist.gov/sites/default/files/css/css_pnbKqRHQnWRII168Jw3PwnUyak1KJaI7c4Tioy53VH0.css?delta=0&language=en&theme=nist_www&include=eJx1kYGuwyAIRX_IVz_JUMuUzYoTXNe_X9utabPlJYbA4QZu0HNFe703rLPpwd-c8vKKPeXuKv-2yHM2gTkkdJAhzUpe7DcwmURdonwjdRdKitX-IhfgLRRSpLFUfqD9BquZjWnEERcPnHqobuTBDiTQL2vXoUZmURwXr4Kb3obEPaRz_vcZZSPCgHUv3TRNZ_WpXiX41HWBHWorkLpPaQpUCBVKlL1zkK7l0vpEEnEwD8JJ7Ba7xXVLaPzxBx1nj-ZCwUNR4rxf6yBvy3hvkFxEClEPlyP5yuuxXmYwua8"/> <link rel="stylesheet" media="all" href="/web/20231209224628cs_/https://www.nist.gov/sites/default/files/css/css_6prwlieMvitJqVLptJ59w_NxX2prM0abXhYVoH12prk.css?delta=1&language=en&theme=nist_www&include=eJx1kYGuwyAIRX_IVz_JUMuUzYoTXNe_X9utabPlJYbA4QZu0HNFe703rLPpwd-c8vKKPeXuKv-2yHM2gTkkdJAhzUpe7DcwmURdonwjdRdKitX-IhfgLRRSpLFUfqD9BquZjWnEERcPnHqobuTBDiTQL2vXoUZmURwXr4Kb3obEPaRz_vcZZSPCgHUv3TRNZ_WpXiX41HWBHWorkLpPaQpUCBVKlL1zkK7l0vpEEnEwD8JJ7Ba7xXVLaPzxBx1nj-ZCwUNR4rxf6yBvy3hvkFxEClEPlyP5yuuxXmYwua8"/> <link rel="stylesheet" media="print" href="/web/20231209224628cs_/https://www.nist.gov/sites/default/files/css/css_6MuKXqcH69mMwmOSjiD2G_c6UXIqUTZ1TRnur95k7Qk.css?delta=2&language=en&theme=nist_www&include=eJx1kYGuwyAIRX_IVz_JUMuUzYoTXNe_X9utabPlJYbA4QZu0HNFe703rLPpwd-c8vKKPeXuKv-2yHM2gTkkdJAhzUpe7DcwmURdonwjdRdKitX-IhfgLRRSpLFUfqD9BquZjWnEERcPnHqobuTBDiTQL2vXoUZmURwXr4Kb3obEPaRz_vcZZSPCgHUv3TRNZ_WpXiX41HWBHWorkLpPaQpUCBVKlL1zkK7l0vpEEnEwD8JJ7Ba7xXVLaPzxBx1nj-ZCwUNR4rxf6yBvy3hvkFxEClEPlyP5yuuxXmYwua8"/> <link rel="stylesheet" media="all" href="/web/20231209224628cs_/https://www.nist.gov/sites/default/files/css/css_zxDJPMpCfrT8NQEavjogRlrVmShwu9oesPd2F7606bk.css?delta=3&language=en&theme=nist_www&include=eJx1kYGuwyAIRX_IVz_JUMuUzYoTXNe_X9utabPlJYbA4QZu0HNFe703rLPpwd-c8vKKPeXuKv-2yHM2gTkkdJAhzUpe7DcwmURdonwjdRdKitX-IhfgLRRSpLFUfqD9BquZjWnEERcPnHqobuTBDiTQL2vXoUZmURwXr4Kb3obEPaRz_vcZZSPCgHUv3TRNZ_WpXiX41HWBHWorkLpPaQpUCBVKlL1zkK7l0vpEEnEwD8JJ7Ba7xXVLaPzxBx1nj-ZCwUNR4rxf6yBvy3hvkFxEClEPlyP5yuuxXmYwua8"/> <script src="/web/20231209224628js_/https://www.nist.gov/sites/default/files/js/js_3ssAdmvsW-btol8ydZT2eloQN8l11yuGacOobfI1-_0.js?scope=header&delta=0&language=en&theme=nist_www&include=eJx1kYGuwyAIRX_IVz_JUMuUzYoTXNe_X9utabPlJYbA4QZu0HNFe703rLPpwd-c8vKKPeXuKv-2yHM2gTkkdJAhzUpe7DcwmURdonwjdRdKitX-IhfgLRRSpLFUfqD9BquZjWnEERcPnHqobuTBDiTQL2vXoUZmURwXr4Kb3obEPaRz_vcZZSPCgHUv3TRNZ_WpXiX41HWBHWorkLpPaQpUCBVKlL1zkK7l0vpEEnEwD8JJ7Ba7xXVLaPzxBx1nj-ZCwUNR4rxf6yBvy3hvkFxEClEPlyP5yuuxXmYwua8"></script> </head> <body class="node-411331"> <a href="#main-content" class="visually-hidden focusable" data-elastic-exclude> Skip to main content </a> <div class="dialog-off-canvas-main-canvas" data-off-canvas-main-canvas>  <section data-elastic-exclude class="usa-banner" aria-label="Official government website"> <div class="usa-accordion"> <header class="usa-banner__header"> <div class="usa-banner__inner"> <div class="grid-col-auto"> <img class="usa-banner__header-flag" src="/web/20231209224628im_/https://www.nist.gov/libraries/nist-component-library/dist/img/us_flag_small.png" alt="U.S. flag"> </div> <div class="grid-col-fill tablet:grid-col-auto"> <p class="usa-banner__header-text">An official website of the United States government</p> <p class="usa-banner__header-action" aria-hidden="true">Here’s how you know</p> </div> <button class="usa-accordion__button usa-banner__button" aria-expanded="false" aria-controls="gov-banner-default"> <span class="usa-banner__button-text">Here’s how you know</span> </button> </div> </header> <div class="usa-banner__content usa-accordion__content" id="gov-banner-default"> <div class="grid-row grid-gap-lg"> <div class="usa-banner__guidance tablet:grid-col-6"> <img class="usa-banner__icon usa-media-block__img" src="/web/20231209224628im_/https://www.nist.gov/libraries/nist-component-library/dist/img/icon-dot-gov.svg" role="img" alt="" aria-hidden="true"> <div class="usa-media-block__body"> <p> <strong>Official websites use .gov</strong> <br/> A <strong>.gov</strong> website belongs to an official government organization in the United States. </p> </div> </div> <div class="usa-banner__guidance tablet:grid-col-6"> <img class="usa-banner__icon usa-media-block__img" src="/web/20231209224628im_/https://www.nist.gov/libraries/nist-component-library/dist/img/icon-https.svg" role="img" alt="" aria-hidden="true"> <div class="usa-media-block__body"> <p> <strong>Secure .gov websites use HTTPS</strong> <br/> A <strong>lock</strong> ( <span class="icon-lock"> <svg xmlns="http://www.w3.org/2000/svg" width="52" height="64" viewbox="0 0 52 64" class="usa-banner__lock-image" role="img" aria-labelledby="banner-lock-title banner-lock-description" focusable="false"> <title id="banner-lock-title">Lock</title> <desc id="banner-lock-description">A locked padlock</desc><path fill="#000000" fill-rule="evenodd" d="M26 0c10.493 0 19 8.507 19 19v9h3a4 4 0 0 1 4 4v28a4 4 0 0 1-4 4H4a4 4 0 0 1-4-4V32a4 4 0 0 1 4-4h3v-9C7 8.507 15.507 0 26 0zm0 8c-5.979 0-10.843 4.77-10.996 10.712L15 19v9h22v-9c0-6.075-4.925-11-11-11z"/></svg> </span> ) or <strong>https://</strong> means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites. </p> </div> </div> </div> </div> </div> </section>  <div data-elastic-exclude>  <div class="nist-print-header" style="display:none;"> <p class="nist-print-header__url">https://www.nist.gov/pml/time-and-frequency-division/time-services</p> <img class="nist-print-header__logo" width="289" height="38" src="/web/20231209224628im_/https://www.nist.gov/libraries/nist-component-library/dist/img/logo/nist_logo_sidestack.svg" alt="National Institute of Standards and Technology"/> </div> <div class="usa-overlay"></div> <header class="usa-header nist-header--www nist-header--minimal" role="banner"> <div class="usa-navbar"> <div class="usa-logo flex-fill"> <a href="/web/20231209224628/https://www.nist.gov/" title="National Institute of Standards and Technology" aria-label="Home"> <img src="/web/20231209224628im_/https://www.nist.gov/libraries/nist-component-library/dist/img/logo/logo.svg" alt="National Institute of Standards and Technology" width="300px" height="80px"/> </a> </div> <div class="usa-header__right grid-row flex-auto"> <div class="grid-col-fill nist-header__search-group"> <form class="usa-search usa-search--small" accept-charset="UTF-8" action="/web/20231209224628/https://www.nist.gov/search" id="search_form" method="get"> <div role="search"> <label class="usa-sr-only" for="search-form">Search NIST</label> <input class="usa-input" id="search-form" type="search" name="s" placeholder="Search NIST" required="" maxlength="128"> <button class="usa-button" type="submit"><img src="/web/20231209224628im_/https://www.nist.gov/libraries/nist-component-library/dist/img/usa-icons-bg/search--white.svg" class="usa-search__submit-icon" alt="Search"></button> </div> </form> </div> <div class="grid-col-auto padding-left-1"> <button class="usa-menu-btn">Menu</button> </div> </div> </div> <nav aria-label="Primary navigation" class="usa-nav"> <div class="usa-nav__inner"> <button class="usa-nav__close">Close</button> <ul class="usa-nav__primary usa-accordion"> <li class="usa-nav__primary-item"> <button class="usa-accordion__button usa-nav__link" aria-expanded="false" aria-controls="primary_menu-1"><span>Topics</span></button> <div id="primary_menu-1" class="usa-nav__submenu usa-megamenu"> <div class="grid-row"> <div class="tablet:grid-col-fill"><ul class="usa-nav__submenu-list"> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/topics" class="usa-nav__link">All Topics</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/advanced-communications" class="usa-nav__link">Advanced communications</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/artificial-intelligence" class="usa-nav__link">Artificial intelligence</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/bioscience" class="usa-nav__link">Bioscience</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/buildings-construction" class="usa-nav__link">Buildings and construction</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/chemistry" class="usa-nav__link">Chemistry</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/climate" class="usa-nav__link">Climate</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/cybersecurity" class="usa-nav__link">Cybersecurity</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/electronics" class="usa-nav__link">Electronics</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/energy" class="usa-nav__link">Energy</a> </li> </ul></div><div class="column-break tablet:grid-col-fill"><ul class="usa-nav__submenu-list"> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/environment" class="usa-nav__link">Environment</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/fire" class="usa-nav__link">Fire</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/forensic-science" class="usa-nav__link">Forensic science</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/health" class="usa-nav__link">Health</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/information-technology" class="usa-nav__link">Information technology</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/infrastructure" class="usa-nav__link">Infrastructure</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/manufacturing" class="usa-nav__link">Manufacturing</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/materials" class="usa-nav__link">Materials</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/mathematics-statistics" class="usa-nav__link">Mathematics and statistics</a> </li> </ul></div><div class="column-break tablet:grid-col-fill"><ul class="usa-nav__submenu-list"> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/metrology" class="usa-nav__link">Metrology</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/nanotechnology" class="usa-nav__link">Nanotechnology</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/neutron-research" class="usa-nav__link">Neutron research</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/performance-excellence" class="usa-nav__link">Performance excellence</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/physics" class="usa-nav__link">Physics</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/public-safety" class="usa-nav__link">Public safety</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/resilience" class="usa-nav__link">Resilience</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/standards" class="usa-nav__link">Standards</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/transportation" class="usa-nav__link">Transportation</a> </li> </ul> </div> </div> </div> </li> <li class="usa-nav__primary-item"> <a class="usa-nav__link" href="/web/20231209224628/https://www.nist.gov/publications">Publications</a> </li> <li class="usa-nav__primary-item"> <button class="usa-accordion__button usa-nav__link" aria-expanded="false" aria-controls="primary_menu-3"><span>Labs & Major Programs</span></button> <div id="primary_menu-3" class="usa-nav__submenu usa-megamenu"> <div class="grid-row"> <div class="tablet:grid-col-fill"><ul class="usa-nav__submenu-list"> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/labs-major-programs/laboratories" class="usa-nav__link">Laboratories</a> <ul class="usa-nav__submenu-list"> <li> <a href="/web/20231209224628/https://www.nist.gov/ctl" class="usa-nav__link">Communications Technology Laboratory</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/el" class="usa-nav__link">Engineering Laboratory</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/itl" class="usa-nav__link">Information Technology Laboratory</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/mml" class="usa-nav__link">Material Measurement Laboratory</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/pml" class="usa-nav__link">Physical Measurement Laboratory</a> </li> </ul> </li> </ul></div><div class="column-break tablet:grid-col-fill"><ul class="usa-nav__submenu-list"> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/labs-major-programs/user-facilities" class="usa-nav__link">User Facilities</a> <ul class="usa-nav__submenu-list"> <li> <a href="/web/20231209224628/https://www.nist.gov/ncnr" class="usa-nav__link">NIST Center for Neutron Research</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/cnst" class="usa-nav__link">CNST NanoFab</a> </li> </ul> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/labs-major-programs/research-test-beds" class="usa-nav__link">Research Test Beds</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/laboratories/projects-programs" class="usa-nav__link">Research Projects</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/laboratories/tools-instruments" class="usa-nav__link">Tools & Instruments</a> </li> </ul></div><div class="column-break tablet:grid-col-fill"><ul class="usa-nav__submenu-list"> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/labs-major-programs/major-programs" class="usa-nav__link">Major Programs</a> <ul class="usa-nav__submenu-list"> <li> <a href="/web/20231209224628/https://www.nist.gov/baldrige" class="usa-nav__link">Baldrige Performance Excellence Program</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/chips" class="usa-nav__link">CHIPS for America Initiative</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/mep" class="usa-nav__link">Manufacturing Extension Partnership (MEP)</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/oam" class="usa-nav__link">Office of Advanced Manufacturing</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/spo" class="usa-nav__link">Special Programs Office</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/tpo" class="usa-nav__link">Technology Partnerships Office</a> </li> </ul> </li> </ul> </div> </div> </div> </li> <li class="usa-nav__primary-item"> <button class="usa-accordion__button usa-nav__link usa-current" aria-expanded="false" aria-controls="primary_menu-4"><span>Services & Resources</span></button> <div id="primary_menu-4" class="usa-nav__submenu usa-megamenu"> <div class="grid-row"> <div class="tablet:grid-col-fill"><ul class="usa-nav__submenu-list"> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/services-resources/standards-and-measurements" class="usa-nav__link usa-current">Standards and Measurements</a> <ul class="usa-nav__submenu-list"> <li> <a href="/web/20231209224628/https://www.nist.gov/calibrations" class="usa-nav__link">Calibration Services</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/nvlap" class="usa-nav__link">Laboratory Accreditation (NVLAP)</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/nist-quality-system" class="usa-nav__link">Quality System</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/srm" class="usa-nav__link">Standard Reference Materials (SRMs)</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/standardsgov" class="usa-nav__link">Standards.gov</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-services" class="usa-nav__link usa-current">Time Services</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/pml/owm" class="usa-nav__link">Office of Weights and Measures</a> </li> </ul> </li> </ul></div><div class="column-break tablet:grid-col-fill"><ul class="usa-nav__submenu-list"> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/services-resources/software" class="usa-nav__link">Software</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/data" class="usa-nav__link">Data</a> <ul class="usa-nav__submenu-list"> <li> <a href="https://web.archive.org/web/20231209224628/https://webbook.nist.gov/chemistry/" class="usa-nav__link">Chemistry WebBook</a> </li> <li> <a href="https://web.archive.org/web/20231209224628/https://nvd.nist.gov/" class="usa-nav__link">National Vulnerability Database</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/pml/productsservices/physical-reference-data" class="usa-nav__link">Physical Reference Data</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/srd" class="usa-nav__link">Standard Reference Data (SRD)</a> </li> </ul> </li> <li class="usa-nav__submenu-item"> <a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/shop" class="usa-nav__link">Storefront</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/tpo" class="usa-nav__link">License & Patents</a> </li> </ul></div><div class="column-break tablet:grid-col-fill"><ul class="usa-nav__submenu-list"> <li class="usa-nav__submenu-item"> <a href="https://web.archive.org/web/20231209224628/https://csrc.nist.gov/" class="usa-nav__link">Computer Security Resource Center (CSRC)</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/nist-research-library" class="usa-nav__link">NIST Research Library</a> </li> </ul> </div> </div> </div> </li> <li class="usa-nav__primary-item"> <button class="usa-accordion__button usa-nav__link" aria-expanded="false" aria-controls="primary_menu-5"><span>News & Events</span></button> <div id="primary_menu-5" class="usa-nav__submenu usa-megamenu"> <div class="grid-row"> <div class="tablet:grid-col-fill"><ul class="usa-nav__submenu-list"> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/news-events/news" class="usa-nav__link">News</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/news-events/events" class="usa-nav__link">Events</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/blogs" class="usa-nav__link">Blogs</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/feature-stories" class="usa-nav__link">Feature Stories</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/awards" class="usa-nav__link">Awards</a> </li> </ul></div><div class="column-break tablet:grid-col-fill"><ul class="usa-nav__submenu-list"> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/video-gallery" class="usa-nav__link">Video Gallery</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/image-gallery" class="usa-nav__link">Image Gallery</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/pao/media-contacts" class="usa-nav__link">Media Contacts</a> </li> </ul> </div> </div> </div> </li> <li class="usa-nav__primary-item"> <button class="usa-accordion__button usa-nav__link" aria-expanded="false" aria-controls="primary_menu-6"><span>About NIST</span></button> <div id="primary_menu-6" class="usa-nav__submenu usa-megamenu"> <div class="grid-row"> <div class="tablet:grid-col-fill"><ul class="usa-nav__submenu-list"> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/about-nist" class="usa-nav__link">About Us</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/about-nist/contact-us" class="usa-nav__link">Contact Us</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/about-nist/visit" class="usa-nav__link">Visit</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/careers" class="usa-nav__link">Careers</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/director/nist-organization-structure" class="usa-nav__link">Our Organization</a> <ul class="usa-nav__submenu-list"> <li> <a href="/web/20231209224628/https://www.nist.gov/director" class="usa-nav__link">Office of the Director</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/director/nist-organization-structure/budget-planning" class="usa-nav__link">Budget & Planning</a> </li> </ul> </li> </ul></div><div class="column-break tablet:grid-col-fill"><ul class="usa-nav__submenu-list"> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/about-nist/work-nist" class="usa-nav__link">Work with NIST</a> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/history" class="usa-nav__link">History</a> <ul class="usa-nav__submenu-list"> <li> <a href="https://web.archive.org/web/20231209224628/http://nistdigitalarchives.contentdm.oclc.org/" class="usa-nav__link">NIST Digital Archives</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/nist-museum" class="usa-nav__link">NIST Museum</a> </li> <li> <a href="/web/20231209224628/https://www.nist.gov/nist-and-nobel" class="usa-nav__link">NIST and the Nobel</a> </li> </ul> </li> <li class="usa-nav__submenu-item"> <a href="/web/20231209224628/https://www.nist.gov/education" class="usa-nav__link">Educational Resources</a> </li> </ul> </div> </div> </div> </li> </ul> </div> </nav> </header>  </div> <div class="grid-container"> <div data-drupal-messages-fallback class="hidden"></div> </div> <div id="block-nist-www-content" class="nist-block"> <section class="nist-page__content usa-section clearfix"> <a id="main-content" tabindex="-1"></a> <div class="nist-section-header nist-section-header--menu"> <div class="nist-section-header__top grid-container"> <a href="/web/20231209224628/https://www.nist.gov/pml">Physical Measurement Laboratory</a> /<a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division">Time and Frequency Division</a> </div> <div class="nist-section-header__sub"> <div class="nist-section-header__main grid-container"> <div class="grid-row"> <div class="nist-section-header__title tablet-lg:grid-col-4"> <h1 class="nist-page__title">Time Realization and Distribution Group</h1> </div> <div class="nist-section-header__desc tablet-lg:grid-col-8"> <div class="text-with-summary"> <p>The Time Realization and Distribution group distributes standard time and frequency signals generated by the Coordinated Universal Time scale, UTC(NIST), maintained at the NIST laboratories in Boulder, Colorado. UTC(NIST) is the U. S. national standard for time-of-day, time interval, and frequency.</p> </div> </div> </div> </div> </div> </div> <div class="grid-container margin-top-4"> <div class="grid-row grid-gap-6"> <aside class="nist-page__region nist-page__region--sidebar-first tablet-lg:grid-col-4 desktop-lg:grid-col-3"> <div>  <div data-elastic-exclude="" class="nist-block"> <nav> <ul class="usa-sidenav usa-accordion "> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml" data-drupal-link-system-path="">Laboratory Homepage</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division" data-drupal-link-system-path="">Division Homepage</a> </li> <li class="usa-sidenav__item"> <a href="https://web.archive.org/web/20231209224628/http://time.gov/" data-drupal-link-system-path="">Official United States Time</a> </li> <li class="usa-sidenav__item usa-sidenav__item--parent"> <a href="/web/20231209224628/https://www.nist.gov/org/time-and-frequency-division/groups" class="usa-current" data-drupal-link-system-path="">Groups</a> <button class="usa-accordion__button" aria-expanded="true" aria-controls="menu-time-and-frequency-4"><span class="usa-sr-only">Expand or Collapse</span></button> <ul id="menu-time-and-frequency-4" class="usa-sidenav__sublist usa-accordion"> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/atomic-devices-and-instrumentation" data-drupal-link-system-path="">Atomic Devices and Instrumentation</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/ion-storage" data-drupal-link-system-path="">Ion Storage</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/neutral-atom-optical-clocks" data-drupal-link-system-path="">Neutral Atom Optical Clocks</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-and-frequency-metrology" data-drupal-link-system-path="">Phase Noise Metrology</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/precision-photonic-synthesis" data-drupal-link-system-path="">Precision Photonic Synthesis</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/quantum-nonlinear-nanophotonics" data-drupal-link-system-path="">Quantum & Nonlinear Nanophotonics</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-services" class="usa-current" data-drupal-link-system-path="">Time Realization and Distribution</a> </li> </ul> </li> <li class="usa-sidenav__item"> <a href="https://web.archive.org/web/20231209224628/https://tf.nist.gov/general/publications.htm" data-drupal-link-system-path="">Publications</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/staff/division/5961" data-drupal-link-system-path="">Staff Directory</a> </li> <li class="usa-sidenav__item usa-sidenav__item--parent"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-distribution" data-drupal-link-system-path="">Time Distribution</a> <button class="usa-accordion__button" aria-expanded="false" aria-controls="menu-time-and-frequency-7"><span class="usa-sr-only">Expand or Collapse</span></button> <ul id="menu-time-and-frequency-7" class="usa-sidenav__sublist usa-accordion"> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-distribution/automated-computer-time-service-acts" data-drupal-link-system-path="">Automated Computer Time Service (ACTS)</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/services/gps-data-archive" data-drupal-link-system-path="">GPS Data Archive</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/time-distribution/gps-time-transfer" data-drupal-link-system-path="">GPS Time Transfer</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-distribution/internet-time-service-its" data-drupal-link-system-path="">Internet Time Service (ITS)</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-distribution/radio-station-wwv" data-drupal-link-system-path="">Radio Station WWV</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-distribution/radio-station-wwvb" data-drupal-link-system-path="">Radio Station WWVB</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-distribution/radio-station-wwvh" data-drupal-link-system-path="">Radio Station WWVH</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/programs-projects/frequency-measurement-and-analysis-service-fmas" data-drupal-link-system-path="">Remote Frequency Calibrations (FMAS)</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/programs-projects/time-measurement-and-analysis-service-tmas" data-drupal-link-system-path="">Remote Time Calibrations (TMAS)</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-distribution/radio-station-wwv/telephone-time-day-service" data-drupal-link-system-path="">Telephone Time-of-Day (TTDS)</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-distribution/two-way-satellite-time-and-frequency-transfer" data-drupal-link-system-path="">Two-Way Satellite Time and Frequency Transfer (TWSTFT)</a> </li> </ul> </li> <li class="usa-sidenav__item usa-sidenav__item--parent"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-realization" data-drupal-link-system-path="">Time Realization</a> <button class="usa-accordion__button" aria-expanded="false" aria-controls="menu-time-and-frequency-8"><span class="usa-sr-only">Expand or Collapse</span></button> <ul id="menu-time-and-frequency-8" class="usa-sidenav__sublist usa-accordion"> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-realization/leap-seconds" data-drupal-link-system-path="">Leap Seconds</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-realization/cesium-fountain-atomic-clocks" data-drupal-link-system-path="">Cesium Fountain Atomic Clocks</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-realization/time-scale-data-and-bulletin-archive" data-drupal-link-system-path="">Time Scale Data and Bulletin Archive</a> </li> <li class="usa-sidenav__item"> <a href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-realization/utcnist-time-scale-0" data-drupal-link-system-path="">UTC(NIST) Time Scale</a> </li> </ul> </li> </ul> </nav> </div>  </div> </aside> <div class="nist-page__region nist-page__region--content tablet-lg:grid-col-8 desktop-lg:grid-col-9"> <div class="nist-block"> <div class="paragraph paragraph--type--hero paragraph--view-mode--default"> <div class="nist-hero grid-row grid-gap-2"> <div class="nist-hero__item tablet:grid-col-12 "> <div class="nist-hero__item-inner"> <div class="nist-hero__image"> <a href=""> <picture> <source srcset="/web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/1200_wide/public/images/2023/05/20/time-realization-and-distribution-group.png.webp?itok=bjCBOE-K 1x, /web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/2400_wide/public/images/2023/05/20/time-realization-and-distribution-group.png.webp?itok=Tki57h5D 2x" media="(min-width: 1200px)" type="image/webp" width="1200" height="799"/> <source srcset="/web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/600_wide/public/images/2023/05/20/time-realization-and-distribution-group.png.webp?itok=uWp9hRF7 1x, /web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/1200_wide/public/images/2023/05/20/time-realization-and-distribution-group.png.webp?itok=bjCBOE-K 2x" media="(min-width: 480px)" type="image/webp" width="600" height="399"/> <source srcset="/web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/300_wide/public/images/2023/05/20/time-realization-and-distribution-group.png.webp?itok=m8NpNho3 1x, /web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/600_wide/public/images/2023/05/20/time-realization-and-distribution-group.png.webp?itok=uWp9hRF7 2x" media="(min-width: 0px)" type="image/webp" width="300" height="200"/> <img loading="eager" src="/web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/1200_wide/public/images/2023/05/20/time-realization-and-distribution-group.png.jpg?itok=bjCBOE-K" width="1200" height="799" alt="time realization and distribution group members" typeof="foaf:Image"/> </picture> </a> </div> <div class="nist-hero__caption"> <a href=""> <div class="text">Time Realization and Distribution Group</div> </a> </div> </div> </div> </div> </div> <div class="nist-content-row nist-content-row--width-legible paragraph paragraph--type--text paragraph--view-mode--default"> <div class="nist-block text-long"><p>One of NIST's mission essential functions is to provide the United States with official sources of time and frequency. Our group fulfills this mission by operating and continuously analyzing a large ensemble of commercial atomic clocks. Briefly, an atomic clock measures the passage of time by counting oscillations of an electronic signal kept resonant with a state transition in an atom, engineered for insensitivity to the surrounding environment or perturbing effects like magnetic field fluctuations.</p> <p>The stability and robustness of the derived timing signal, called <a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="b2d9874a-d7ae-4aae-bf26-749f4095459f" href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-realization/utcnist-time-scale-0" title="UTC(NIST) Time Scale">UTC(NIST)</a>, is enhanced by averaging across the clock ensemble. The accuracy of UTC(NIST) is ensured by regular comparisons with primary frequency references---devices like the <a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="2886c60e-2b45-48c9-845b-67f69b40e58e" href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-realization/cesium-fountain-atomic-clocks" title="NIST’s Cesium Fountain Atomic Clocks">cesium atomic fountain</a> that attempt to realize a microwave frequency closely based on the definition of the International System (SI) second in terms of an unperturbed state transition in the cesium atom---and by regular comparisons with other national metrology laboratories. We keep UTC(NIST) closely aligned with the international atomic time scale Coordinated Universal Time (UTC); our typical time offsets are at the 1 nanosecond level with frequency offsets of about 1 x 10<sup>-15</sup>.</p> <p>We distribute NIST time and frequency signals freely to the public (e.g. <a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="7f3ea4b1-a4dc-4fb8-ab17-8e78e6a217e4" href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-distribution/internet-time-service-its" title="NIST Internet Time Service (ITS)">the Internet Time Service</a>, <a href="https://web.archive.org/web/20231209224628/https://time.gov/">time.gov website</a>, <a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="1dac7986-4597-4d1f-9dce-523e0d53d147" href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-distribution/radio-station-wwv" title="Radio Station WWV">WWV</a>, <a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="7adae22d-3710-4706-9ef2-8dbb1f049181" href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-distribution/radio-station-wwvb" title="Radio Station WWVB">WWVB</a>, and <a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="c9215bba-0c4a-4c1b-ab72-3a4a5b051045" href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-distribution/radio-station-wwvh" title="Radio Station WWVH">WWVH</a> radio stations). For customers who need UTC(NIST) at higher accuracies or that require a controlled or calibrated transfer medium, we offer remote calibration services (e.g. <a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="d613428d-8936-4bd0-a944-e9694b5b2204" href="/web/20231209224628/https://www.nist.gov/programs-projects/time-measurement-and-analysis-service-tmas" title="Time Measurement and Analysis Service (TMAS)">TMAS</a>, <a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="55c190c4-f711-412e-8424-834ba9f5db46" href="/web/20231209224628/https://www.nist.gov/programs-projects/frequency-measurement-and-analysis-service-fmas" title="Frequency Measurement and Analysis Service (FMAS)">FMAS</a>) and direct links (e.g. <a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="bc8bbac3-cd6e-4a22-b78a-2cba7e7683fa" href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-services/time-over-fiber" title="Time Over Fiber">Time over Fiber</a>, Time over Satellite). We publish measurements of UTC(NIST) against timing signals from the <a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="8ab67339-90bc-40d5-bd63-a9eb5ddbd772" href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/services/gps-data-archive" title="GPS Data Archive">Global Positioning System (GPS)</a>, other global satellite navigation systems (GNSS), and support time transfer methods using GNSS satellites as transfer oscillators. We also offer calibration services for oscillators, commercial atomic clocks, and <a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="7903f3de-5a68-4b37-be3b-eb342b909fbc" href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-services/calibrations-services-time-and-frequency-division" title="Calibrations Services in the Time and Frequency Division">GPS/GNSS receivers</a>. The group supports US industry and other agencies with <a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="312716a4-a83c-4fdb-b6e8-22d4626c5af5" href="/web/20231209224628/https://www.nist.gov/tpo/partnerships/cooperative-research-and-development-agreement-crada" title="Cooperative Research and Development Agreement (CRADA)">Collaborative Research and Development Agreements (CRADAs)</a> and technology transfer partnerships.</p> <p>Finally, the group incorporates state-of-the-art developments in time and frequency metrology, such as <a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="7337be56-acdc-49b3-a9f6-43bec7c2ad5f" href="/web/20231209224628/https://www.nist.gov/programs-projects/trapped-sr-ion-clock-secondary-realization-si-second" title="Trapped Sr+ ion clock; a secondary realization of the SI second">optical atomic clocks</a>, and supports NIST laboratory research programs.</p> <ul><li><a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="b4d1767e-6658-4abb-b863-8d8b77c933eb" href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-distribution" title="Time Distribution">Time Distribution</a></li> <li><a data-entity-substitution="canonical" data-entity-type="node" data-entity-uuid="1e3a9302-75d1-4e3e-a259-793826e42647" href="/web/20231209224628/https://www.nist.gov/pml/time-and-frequency-division/time-realization" title="Time Realization">Time Realization</a></li> </ul></div> </div> <div class="nist-content-row nist-content-row--width-legible paragraph paragraph--type--text paragraph--view-mode--default"> <div class="nist-block text-long"><h2 class="nist-block__title">NBS/NIST Radio Stations: The Story of an Old Timer</h2> <div class="grid-row grid-gap"> <div class="grid-col-3"> <figure class="align-center nist-image"><img alt="NBS/DOC" height="257" loading="lazy" src="/web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/480_x_480_limit/public/images/2017/02/27/nbs-commerce.jpg?itok=FSjn8Gn4" typeof="foaf:Image" width="480"/><figcaption class="nist-image__caption"><div class="nist-image__caption-content" data-caption-editable="true"> </div> </figcaption></figure></div> <div class="grid-col-9"> <p>This <a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/pml/nbsnist-radio-stations-story-old-timer">series of webpages</a> will lead you on a journey on the history of the NBS/NIST radio stations. You can watch a <a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/video/nist-colloquium-nbsnist-radio-stations-story-old-timer">video</a> as well.</p> </div> </div></div> </div> <div class="paragraph paragraph--type--dynamic-content-list-ou paragraph--view-mode--default"> <div class="nist-block "> <h2 class="nist-block__title"> <div class="string">News and Updates</div> </h2> <div class="viewsreference"><div class="views-element-container"><div class="js-view-dom-id-d5d6a8d282e1aafce5898f764ceea41e54650513f1980bcd25f9a169fe62da37"> <div> <article about="/news-events/news/2021/11/nist-recommends-steps-boost-resilience-us-timekeeping" typeof="schema:Article" class="nist-teaser"> <div class="nist-teaser__image"> <div class="entity-reference"> <a href="/web/20231209224628/https://www.nist.gov/news-events/news/2021/11/nist-recommends-steps-boost-resilience-us-timekeeping" hreflang="en"><img loading="lazy" src="/web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/thumbnail/public/images/2021/11/29/resilient_time_image_%28002%29.png?itok=6wlqig_f" width="100" height="32" alt="A small rectangular device with a display screen and buttons sits next to a spool of yellow fiber. " typeof="foaf:Image"/> </a> </div> </div> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20231209224628/https://www.nist.gov/news-events/news/2021/11/nist-recommends-steps-boost-resilience-us-timekeeping"><span property="schema:name">NIST Recommends Steps to Boost Resilience of U.S. Timekeeping</span> </a></h3> <div class="nist-teaser__date"> <div class="daterange"><time datetime="2021-11-29T12:00:00Z">November 29, 2021</time> </div> </div> </header> <div class="nist-teaser__content"> <div property="schema:text" class="text-with-summary"> The nation should bolster research and development of systems that distribute accurate time via fiber-optic cable and radio as part of the effort to back up GPS </div> </div> </div> </article> </div> <div> <article about="/news-events/news/2018/06/nist-atomic-clock-comparison-confirms-key-assumptions-einsteins-elevator" typeof="schema:Article" class="nist-teaser"> <div class="nist-teaser__image"> <div class="entity-reference"> <a href="/web/20231209224628/https://www.nist.gov/news-events/news/2018/06/nist-atomic-clock-comparison-confirms-key-assumptions-einsteins-elevator" hreflang="en"><img loading="lazy" src="/web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/thumbnail/public/images/2018/05/31/18pml021_einstein-elevator-withtext-4000px-wide-hr.jpg?itok=d3ksi8Xf" width="88" height="100" alt="Cartoon with man standing on falling blue cube representing Earth, decorated with clumps of clock faces, with yellow sun at right." typeof="foaf:Image"/> </a> </div> </div> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20231209224628/https://www.nist.gov/news-events/news/2018/06/nist-atomic-clock-comparison-confirms-key-assumptions-einsteins-elevator"><span property="schema:name">NIST Atomic Clock Comparison Confirms Key Assumptions of ‘Einstein’s Elevator’</span> </a></h3> <div class="nist-teaser__date"> <div class="daterange"><time datetime="2018-06-04T12:00:00Z">June 4, 2018</time> </div> </div> </header> <div class="nist-teaser__content"> <div property="schema:text" class="text-with-summary"> By comparing different types of remote atomic clocks, physicists at the National Institute of Standards and Technology (NIST) have performed the most accurate </div> </div> </div> </article> </div> <div> <article about="/news-events/news/2017/11/nists-next-generation-atomic-clocks-may-support-official-timekeeping" typeof="schema:Article" class="nist-teaser"> <div class="nist-teaser__image"> <div class="entity-reference"> <a href="/web/20231209224628/https://www.nist.gov/news-events/news/2017/11/nists-next-generation-atomic-clocks-may-support-official-timekeeping" hreflang="en"><img loading="lazy" src="/web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/thumbnail/public/images/2017/11/16/17pml022_levine-with-time-scale-by-j-burrus_175x170.jpg?itok=K_0prB5m" width="66" height="100" alt="Man with gray hair standing beside computer with digital clock display" typeof="foaf:Image"/> </a> </div> </div> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20231209224628/https://www.nist.gov/news-events/news/2017/11/nists-next-generation-atomic-clocks-may-support-official-timekeeping"><span property="schema:name">NIST’s Next-Generation Atomic Clocks May Support Official Timekeeping</span> </a></h3> <div class="nist-teaser__date"> <div class="daterange"><time datetime="2017-11-16T12:00:00Z">November 16, 2017</time> </div> </div> </header> <div class="nist-teaser__content"> <div property="schema:text" class="text-with-summary"> For more than a decade, the National Institute of Standards and Technology (NIST) has been unveiling experimental next-generation atomic clocks. These clocks </div> </div> </div> </article> </div> <footer> <div class="link-list"><a href="/web/20231209224628/https://www.nist.gov/news-events/news-updates/org/6601">View All News and Updates</a></div> </footer> </div> </div> </div> </div> </div> <div class="paragraph paragraph--type--dynamic-content-list-ou paragraph--view-mode--default"> <div class="nist-block "> <h2 class="nist-block__title"> <div class="string">Projects and Programs</div> </h2> <div class="viewsreference"><div class="views-element-container"><div class="js-view-dom-id-6aa1d06dda06bc403688ce2bba5328f42182fcff9be6bb1e36d11ae134905431"> <div> <article about="/programs-projects/frequency-measurement-and-analysis-service-fmas" class="nist-teaser"> <div class="nist-teaser__image"> <div class="entity-reference"> <a href="/web/20231209224628/https://www.nist.gov/programs-projects/frequency-measurement-and-analysis-service-fmas" hreflang="en"><img loading="lazy" src="/web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/thumbnail/public/images/2016/08/30/nistfmas_1.jpg?itok=UyLlE4-2" width="100" height="78" alt="NIST FMAS" typeof="foaf:Image"/> </a> </div> </div> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20231209224628/https://www.nist.gov/programs-projects/frequency-measurement-and-analysis-service-fmas"><span>Frequency Measurement and Analysis Service (FMAS)</span> </a></h3> <div class="nist-teaser__type"> <div class="nist-badge display-inline-block margin-y-1 nist-badge--blue boolean">Ongoing</div> </div> </header> <div class="nist-teaser__content"> <div class="text-long"> The NIST Frequency Measurement and Analysis Service (FMAS) makes it easy to measure and calibrate any quartz, rubidium, cesium, or hydrogen maser frequency </div> </div> </div> </article> </div> <div> <article about="/programs-projects/time-measurement-and-analysis-service-tmas" class="nist-teaser"> <div class="nist-teaser__image"> <div class="entity-reference"> <a href="/web/20231209224628/https://www.nist.gov/programs-projects/time-measurement-and-analysis-service-tmas" hreflang="en"><img loading="lazy" src="/web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/thumbnail/public/images/2017/12/08/nistdo_chassis.png?itok=4Ns8TBSa" width="100" height="55" alt="NIST disciplined clock chassis" typeof="foaf:Image"/> </a> </div> </div> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20231209224628/https://www.nist.gov/programs-projects/time-measurement-and-analysis-service-tmas"><span>Time Measurement and Analysis Service (TMAS)</span> </a></h3> <div class="nist-teaser__type"> <div class="nist-badge display-inline-block margin-y-1 nist-badge--blue boolean">Ongoing</div> </div> </header> <div class="nist-teaser__content"> <div class="text-long"> The NIST Time Measurement and Analysis Service (TMAS) was designed to serve any organization that is required to maintain an accurate local time standard. The </div> </div> </div> </article> </div> <div> <article about="/programs-projects/trapped-sr-ion-clock-secondary-realization-si-second" class="nist-teaser"> <div class="nist-teaser__image"> <div class="entity-reference"> <a href="/web/20231209224628/https://www.nist.gov/programs-projects/trapped-sr-ion-clock-secondary-realization-si-second" hreflang="en"><img loading="lazy" src="/web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/thumbnail/public/images/2023/05/16/trap-assembly.png?itok=UYBPt7pO" width="100" height="60" alt="trap assembly" typeof="foaf:Image"/> </a> </div> </div> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20231209224628/https://www.nist.gov/programs-projects/trapped-sr-ion-clock-secondary-realization-si-second"><span>Trapped Sr+ ion clock; a secondary realization of the SI second</span> </a></h3> <div class="nist-teaser__type"> <div class="nist-badge display-inline-block margin-y-1 nist-badge--blue boolean">Ongoing</div> </div> </header> <div class="nist-teaser__content"> <div class="text-long"> NIST is constructing a high-uptime optical frequency reference based on a single trapped Sr + ion. The goal of this project is to provide long-term ≤ 1x10 -16 </div> </div> </div> </article> </div> <footer> <div class="link-list"><a href="/web/20231209224628/https://www.nist.gov/laboratories/projects-programs/org/6601">View All Projects/Programs</a></div> </footer> </div> </div> </div> </div> </div> <div class="paragraph paragraph--type--dynamic-content-list-ou paragraph--view-mode--default"> <div class="nist-block "> <h2 class="nist-block__title"> <div class="string">Publications</div> </h2> <div class="viewsreference"><div class="views-element-container"><div class="js-view-dom-id-fb34400890fc4a2273ffc6247609c9b374922ec1f5daf44e06bb9d59c5298b9e"> <div> <article about="/publications/vhfuhf-detection-using-high-angular-momentum-rydberg-states" class="nist-teaser"> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20231209224628/https://www.nist.gov/publications/vhfuhf-detection-using-high-angular-momentum-rydberg-states"><span>VHF/UHF detection using high angular momentum Rydberg states</span> </a></h3> <div class="nist-teaser__date"> <div class="daterange"><time datetime="2023-05-12T12:00:00Z">May 12, 2023</time> </div> </div> <div class="nist-teaser__type"> <div class="nist-field nist-field--label-inline text-long"> <div class="nist-field__label">Author(s)</div> <div class="nist-field__item"><span class="nist-author">Roger Brown</span></div> </div> </div> </header> <div class="nist-teaser__content"> <div class="text-with-summary"> We demonstrate resonant detection of rf electric fields from 240 MHz to 900 MHz (VHF/UHF) using electromagnetically induced transparency with orbital angular </div> </div> </div> </article> </div> <div> <article about="/publications/measuring-frequency-accuracy-and-stability-wwv-and-wwvh" class="nist-teaser"> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20231209224628/https://www.nist.gov/publications/measuring-frequency-accuracy-and-stability-wwv-and-wwvh"><span>Measuring the Frequency Accuracy and Stability of WWV and WWVH</span> </a></h3> <div class="nist-teaser__date"> <div class="daterange"><time datetime="2023-03-01T12:00:00Z">March 1, 2023</time> </div> </div> <div class="nist-teaser__type"> <div class="nist-field nist-field--label-inline text-long"> <div class="nist-field__label">Author(s)</div> <div class="nist-field__item"><span class="nist-author">Michael A. Lombardi</span></div> </div> </div> </header> <div class="nist-teaser__content"> <div class="text-with-summary"> Radio station WWV, famous for the "at the tone ...." announcements broadcast at the top of each minute, is known to shortwave listeners and radio amateurs </div> </div> </div> </article> </div> <div> <article about="/publications/measuring-timing-accuracy-satellite-time-and-location-stl-receivers" class="nist-teaser"> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20231209224628/https://www.nist.gov/publications/measuring-timing-accuracy-satellite-time-and-location-stl-receivers"><span>Measuring the Timing Accuracy of Satellite Time and Location (STL) Receivers</span> </a></h3> <div class="nist-teaser__date"> <div class="daterange"><time datetime="2023-01-23T12:00:00Z">January 23, 2023</time> </div> </div> <div class="nist-teaser__type"> <div class="nist-field nist-field--label-inline text-long"> <div class="nist-field__label">Author(s)</div> <div class="nist-field__item">Peter Johnson, <span class="nist-author">Andrew Novick</span>, <span class="nist-author">Michael A. Lombardi</span></div> </div> </div> </header> <div class="nist-teaser__content"> <div class="text-with-summary"> We present measurements of the timing accuracy and stability of Satellite Time and Location (STL) receivers with respect to UTC(NIST), the coordinated universal </div> </div> </div> </article> </div> <div> <article about="/publications/multi-source-common-view-disciplined-clock-fail-safe-clock-critical-infrastructure" class="nist-teaser"> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20231209224628/https://www.nist.gov/publications/multi-source-common-view-disciplined-clock-fail-safe-clock-critical-infrastructure"><span>Multi-Source Common-View Disciplined Clock: A Fail-Safe Clock for Critical Infrastructure Systems</span> </a></h3> <div class="nist-teaser__date"> <div class="daterange"><time datetime="2022-01-10T12:00:00Z">January 10, 2022</time> </div> </div> <div class="nist-teaser__type"> <div class="nist-field nist-field--label-inline text-long"> <div class="nist-field__label">Author(s)</div> <div class="nist-field__item"><span class="nist-author">Michael A. Lombardi</span></div> </div> </div> </header> <div class="nist-teaser__content"> <div class="text-with-summary"> The multi-source common-view disciplined clock (MSCVDC) is a recent NIST invention designed to support critical infrastructure timing systems that require a </div> </div> </div> </article> </div> <footer> <div class="link-list"><a href="/web/20231209224628/https://www.nist.gov/publications/search/all">View All Publications</a></div> </footer> </div> </div> </div> </div> </div> <div class="paragraph paragraph--type--dynamic-content-list-ou paragraph--view-mode--default"> <div class="nist-block "> <h2 class="nist-block__title"> <div class="string">Awards</div> </h2> <div class="viewsreference"><div class="views-element-container"><div class="js-view-dom-id-6fdb16b68301ff90150f86e3eb6342d73344b64753590a19b120e8e2f1c923ec"> <div> <article about="/awards/2023-distinguished-associate-award-vladislav-gerginov" class="nist-teaser"> <div class="nist-teaser__image"> <div class="entity-reference"> <a href="/web/20231209224628/https://www.nist.gov/awards/2023-distinguished-associate-award-vladislav-gerginov" hreflang="en"><img loading="lazy" src="/web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/thumbnail/public/images/2023/04/26/Gerginov.png?itok=L6HKOoSg" width="100" height="56" alt="Vladi Gerginov" typeof="foaf:Image"/> </a> </div> </div> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20231209224628/https://www.nist.gov/awards/2023-distinguished-associate-award-vladislav-gerginov"><span>2023 Distinguished Associate Award - Vladislav Gerginov</span> </a></h3> </header> <div class="nist-teaser__content"> <div class="text-long"> For long-term and extraordinary contributions in support of NIST’s atomic clock and sensing programs. </div> </div> </div> </article> </div> <div> <article about="/awards/distinguished-ptti-service-award-michael-lombardi" class="nist-teaser"> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20231209224628/https://www.nist.gov/awards/distinguished-ptti-service-award-michael-lombardi"><span>Distinguished PTTI Service Award - Michael A. Lombardi</span> </a></h3> </header> <div class="nist-teaser__content"> <div class="text-long"> Mr. Lombardi was recognized for system development and leadership in the successful delivery of the U.S. time and frequency standards </div> </div> </div> </article> </div> <div> <article about="/nist-awards/2020-edward-uhler-condon-award-glenn-nelson" class="nist-teaser"> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20231209224628/https://www.nist.gov/nist-awards/2020-edward-uhler-condon-award-glenn-nelson"><span>2020 - Edward Uhler Condon Award---Glenn Nelson</span> </a></h3> </header> <div class="nist-teaser__content"> <div class="string-long">For his exemplary historical review article commemorating the 100th anniversary of NIST radio station WWV.</div> </div> </div> </article> </div> <div> <article about="/awards/2019-distinguished-associate-award-jian-yao" class="nist-teaser"> <div class="nist-teaser__image"> <div class="entity-reference"> <a href="/web/20231209224628/https://www.nist.gov/awards/2019-distinguished-associate-award-jian-yao" hreflang="en"><img loading="lazy" src="/web/20231209224628im_/https://www.nist.gov/sites/default/files/styles/thumbnail/public/images/2020/06/22/JianYaoPhoto%20-%20Copy.png?itok=1ER5fZCU" width="79" height="100" alt="Jian Yao" typeof="foaf:Image"/> </a> </div> </div> <div class="nist-teaser__content-wrapper"> <header> <h3 class="nist-teaser__title"><a href="/web/20231209224628/https://www.nist.gov/awards/2019-distinguished-associate-award-jian-yao"><span>2019 Distinguished Associate Award - Jian Yao</span> </a></h3> </header> <div class="nist-teaser__content"> <div class="text-long"> For creating and networking the world's best optical atomic clocks for a 100-fold improvement in precision timekeeping over state of the art </div> </div> </div> </article> </div> <footer> <div class="link-list"><a href="/web/20231209224628/https://www.nist.gov/awards/org/6601">View All Awards</a></div> </footer> </div> </div> </div> </div> </div> </div> </div> </div> </div> <div class="grid-row"> <div class="nist-resource-block nist-resource-block--first tablet:grid-col"> <div class="nist-resource-block__title-bar"> <div class="nist-resource-block__title"> <div class="nist-resource-block__icon"> <img aria-hidden="true" role="img" alt="decorative icon" src="/web/20231209224628im_/https://www.nist.gov/themes/custom/nist_www/img/resource-icons/link-icon-2x.png"/> </div> <h2> <div class="string">SIM Time Scale</div> </h2> </div> </div> <div class="nist-resource-block__content"> <div class="nist-block"> <div class="text-long"><p>To support time and frequency metrology throughout the Americas, the Sistema Interamericano de Metrologia (SIM) Time and Frequency Metrology Working Group (TFMWG) maintains the SIM time scale (SIMT), the first continuously maintained multi-national ensemble time scale that is generated and published in real time (updated every hour). SIMT complements the world's official time scale, Coordinated Universal Time (UTC), by providing real time support to operational timing and calibration systems in the SIM region. The stability of SIMT is superior to most SIM local time scales and SIMT also provides a good approximation of UTC timing accuracy (±15 ns).</p> <p><a href="https://web.archive.org/web/20231209224628/http://tf.nist.gov/sim/">View website >></a></p></div> </div> </div> </div> <div class="nist-resource-block nist-resource-block--second nist-resource-block--green tablet:grid-col"> <div class="nist-resource-block__title-bar"> <div class="nist-resource-block__title"> <div class="nist-resource-block__icon"> <img aria-hidden="true" role="img" alt="decorative icon" src="/web/20231209224628im_/https://www.nist.gov/themes/custom/nist_www/img/resource-icons/product-icon-2x.png"/> </div> <h2> <div class="string">Standard Reference Instruments (SRI)</div> </h2> </div> </div> <div class="nist-resource-block__content"> <div class="nist-block"> <div class="text-long"><p><span>NIST is consolidating its provision of reference instrumentation and devices into a new Standard Reference Instrumentation (SRI) program.</span></p> <p><a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/sri"><span>View website>></span></a></p></div> </div> </div> </div> </div> <div class="grid-container"> <div class="nist-page__region nist-page__region--content-bottom"> <div class="nist-block nist-block--contact"> <h2 class="nist-block__title">Contacts</h2> <div class="nist-contact"> <h3 class="nist-contact__heading">Group Leader</h3> <ul class="nist-contact__items"> <li about="/people/michael-lombardi" class="nist-contact__item"> <div class="nist-contact__name"><a href="/web/20231209224628/https://www.nist.gov/people/michael-lombardi" title="View staff profile page">Michael A. Lombardi</a></div> <div> <a href="https://web.archive.org/web/20231209224628/mailto:michael.lombardi@nist.gov">michael.lombardi@nist.gov</a> </div> <div> (303) 497-3212 </div> </li> </ul> </div> <div class="nist-contact"> <h3 class="nist-contact__heading">Staff</h3> <ul class="nist-contact__items"> <li about="/people/ladan-arissian" class="nist-contact__item"> <div class="nist-contact__name"><a href="/web/20231209224628/https://www.nist.gov/people/ladan-arissian" title="View staff profile page">Ladan Arissian</a></div> <div> <a href="https://web.archive.org/web/20231209224628/mailto:ladan.arissian@nist.gov">ladan.arissian@nist.gov</a> </div> <div> (303) 497-5110 </div> </li> <li about="/people/roger-brown" class="nist-contact__item"> <div class="nist-contact__name"><a href="/web/20231209224628/https://www.nist.gov/people/roger-brown" title="View staff profile page">Roger Brown</a></div> <div> <a href="https://web.archive.org/web/20231209224628/mailto:roger.brown@nist.gov">roger.brown@nist.gov</a> </div> <div> (303) 497-6971 </div> </li> <li about="/people/tom-heavner" class="nist-contact__item"> <div class="nist-contact__name"><a href="/web/20231209224628/https://www.nist.gov/people/tom-heavner" title="View staff profile page">Tom Heavner</a></div> <div> <a href="https://web.archive.org/web/20231209224628/mailto:tom.heavner@nist.gov">tom.heavner@nist.gov</a> </div> <div> (303) 497-5015 </div> </li> <li about="/people/gregory-hoth" class="nist-contact__item"> <div class="nist-contact__name"><a href="/web/20231209224628/https://www.nist.gov/people/gregory-hoth" title="View staff profile page">Gregory Hoth</a></div> <div> <a href="https://web.archive.org/web/20231209224628/mailto:gregory.hoth@nist.gov">gregory.hoth@nist.gov</a> </div> <div> (303) 497-4414 </div> </li> <li about="/people/aidan-montare" class="nist-contact__item"> <div class="nist-contact__name"><a href="/web/20231209224628/https://www.nist.gov/people/aidan-montare" title="View staff profile page">Aidan Montare</a></div> <div> <a href="https://web.archive.org/web/20231209224628/mailto:aidan.montare@nist.gov">aidan.montare@nist.gov</a> </div> <div> (303) 497-5259 </div> </li> <li about="/people/andrew-novick" class="nist-contact__item"> <div class="nist-contact__name"><a href="/web/20231209224628/https://www.nist.gov/people/andrew-novick" title="View staff profile page">Andrew Novick</a></div> <div> <a href="https://web.archive.org/web/20231209224628/mailto:andrew.novick@nist.gov">andrew.novick@nist.gov</a> </div> <div> (303) 497-3378 </div> </li> <li about="/people/bijunath-r-patla" class="nist-contact__item"> <div class="nist-contact__name"><a href="/web/20231209224628/https://www.nist.gov/people/bijunath-r-patla" title="View staff profile page">Bijunath R. Patla</a></div> <div> <a href="https://web.archive.org/web/20231209224628/mailto:bijunath.patla@nist.gov">bijunath.patla@nist.gov</a> </div> <div> (303) 497-4082 </div> </li> <li about="/people/vladislav-gerginov" class="nist-contact__item"> <div class="nist-contact__name"><a href="/web/20231209224628/https://www.nist.gov/people/vladislav-gerginov" title="View staff profile page">Vladislav Gerginov</a></div> <div> <a href="https://web.archive.org/web/20231209224628/mailto:vladislav.gerginov@nist.gov">vladislav.gerginov@nist.gov</a> </div> <div> (303) 497-7366 </div> </li> <li about="/people/tom-parker" class="nist-contact__item"> <div class="nist-contact__name"><a href="/web/20231209224628/https://www.nist.gov/people/tom-parker" title="View staff profile page">Tom Parker</a></div> <div> <a href="https://web.archive.org/web/20231209224628/mailto:tom.parker@nist.gov">tom.parker@nist.gov</a> </div> <div> (303) 497-7881 </div> </li> </ul> </div> <div class="nist-contact"> <h3 class="nist-contact__heading">Radio Station Staff</h3> <ul class="nist-contact__items"> <li about="/people/matthew-j-deutch" class="nist-contact__item"> <div class="nist-contact__name"><a href="/web/20231209224628/https://www.nist.gov/people/matthew-j-deutch" title="View staff profile page">Matthew J. Deutch</a></div> <div> <a href="https://web.archive.org/web/20231209224628/mailto:matthew.deutch@nist.gov">matthew.deutch@nist.gov</a> </div> <div> (303) 497-3914 </div> </li> <li about="/people/glenn-nelson" class="nist-contact__item"> <div class="nist-contact__name"><a href="/web/20231209224628/https://www.nist.gov/people/glenn-nelson" title="View staff profile page">Glenn Nelson</a></div> <div> <a href="https://web.archive.org/web/20231209224628/mailto:glenn.nelson@nist.gov">glenn.nelson@nist.gov</a> </div> <div> (303) 497-3914 </div> </li> <li about="/people/william-yates" class="nist-contact__item"> <div class="nist-contact__name"><a href="/web/20231209224628/https://www.nist.gov/people/william-yates" title="View staff profile page">William Yates</a></div> <div> <a href="https://web.archive.org/web/20231209224628/mailto:william.yates@nist.gov">william.yates@nist.gov</a> </div> <div> (303) 497-3914 </div> </li> <li about="/people/chris-fujita" class="nist-contact__item"> <div class="nist-contact__name"><a href="/web/20231209224628/https://www.nist.gov/people/chris-fujita" title="View staff profile page">Chris Fujita</a></div> <div> <a href="https://web.archive.org/web/20231209224628/mailto:chris.fujita@nist.gov">chris.fujita@nist.gov</a> </div> <div> (808) 335-4361 </div> </li> </ul> </div> </div> </div> </div> </section> </div> <div data-elastic-exclude>  <footer class="nist-footer padding-bottom-4"> <div class="grid-container nist-footer__info"> <div class="grid-row"> <div class="tablet:grid-col-6"> <div class="nist-footer__logo"> <a href="/web/20231209224628/https://www.nist.gov/" title="National Institute of Standards and Technology" rel="home"> <img class="nist-footer__logo-img" src="/web/20231209224628im_/https://www.nist.gov/libraries/nist-component-library/dist/img/logo/NIST-Logo-Brand-White.svg" alt="National Institute of Standards and Technology logo" width="300px" height="42px"/> </a> </div> <div class="nist-footer__contact"> <h3 class="nist-footer__contact-heading">HEADQUARTERS</h3> <address> 100 Bureau Drive<br> Gaithersburg, MD 20899<br> <a href="https://web.archive.org/web/20231209224628/tel:301-975-2000">301-975-2000</a> </address> <p> <a href="https://web.archive.org/web/20231209224628/mailto:do-webmaster@nist.gov">Webmaster</a> | <a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/about-nist/contact-us">Contact Us</a> | <a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/visit">Our Other Offices</a> </p> </div> </div> <div class="tablet:grid-col-6"> <div class="nist-footer__social-links"> <a class="nist-social nist-social--twitter-white" href="https://web.archive.org/web/20231209224628/https://twitter.com/NIST"> <span>Twitter</span> </a> <a class="nist-social nist-social--facebook-white" href="https://web.archive.org/web/20231209224628/https://www.facebook.com/NIST"> <span>Facebook</span> </a> <a class="nist-social nist-social--linkedin-white" href="https://web.archive.org/web/20231209224628/https://www.linkedin.com/company/nist"> <span>LinkedIn</span> </a> <a class="nist-social nist-social--instagram-white" href="https://web.archive.org/web/20231209224628/https://www.instagram.com/nist/"> <span>Instagram</span> </a> <a class="nist-social nist-social--youtube-white" href="https://web.archive.org/web/20231209224628/https://www.youtube.com/NIST"> <span>YouTube</span> </a> <a class="nist-social nist-social--giphy-white" href="https://web.archive.org/web/20231209224628/https://giphy.com/nist"> <span>Giphy</span> </a> <a class="nist-social nist-social--rss-white" href="https://web.archive.org/web/20231209224628/https://www.nist.gov/news-events/nist-rss-feeds"> <span>RSS Feed</span> </a> <a class="nist-social nist-social--envelope-white" href="https://web.archive.org/web/20231209224628/https://public.govdelivery.com/accounts/USNIST/subscriber/new"> <span>Mailing List</span> </a> </div> <div class="nist-footer__feedback"> How are we doing? <a class="usa-button" rel="nofollow" href="/web/20231209224628/https://www.nist.gov/form/nist-gov-feedback?destination=/pml/time-and-frequency-division/time-services" title="Provide feedback">Feedback</a> </div> </div> </div> </div> <div class="grid-container"> <div class="nist-footer__nav" role="navigation"> <ul> <li class="nist-footer__menu-item"> <a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/privacy-policy">Site Privacy</a> </li> <li class="nist-footer__menu-item"> <a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/oism/accessibility">Accessibility</a> </li> <li class="nist-footer__menu-item"> <a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/privacy">Privacy Program</a> </li> <li class="nist-footer__menu-item"> <a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/oism/copyrights">Copyrights</a> </li> <li class="nist-footer__menu-item"> <a href="https://web.archive.org/web/20231209224628/https://www.commerce.gov/vulnerability-disclosure-policy">Vulnerability Disclosure</a> </li> <li class="nist-footer__menu-item"> <a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/no-fear-act-policy">No Fear Act Policy</a> </li> <li class="nist-footer__menu-item"> <a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/office-director/freedom-information-act">FOIA</a> </li> <li class="nist-footer__menu-item"> <a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/environmental-policy-statement">Environmental Policy</a> </li> <li class="nist-footer__menu-item"> <a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/summary-report-scientific-integrity">Scientific Integrity</a> </li> <li class="nist-footer__menu-item"> <a href="https://web.archive.org/web/20231209224628/https://www.nist.gov/nist-information-quality-standards">Information Quality Standards</a> </li> <li class="nist-footer__menu-item"> <a href="https://web.archive.org/web/20231209224628/https://www.commerce.gov/">Commerce.gov</a> </li> <li class="nist-footer__menu-item"> <a href="https://web.archive.org/web/20231209224628/http://www.science.gov/">Science.gov</a> </li> <li class="nist-footer__menu-item"> <a href="https://web.archive.org/web/20231209224628/http://www.usa.gov/">USA.gov</a> </li> <li class="nist-footer__menu-item"> <a href="https://web.archive.org/web/20231209224628/https://vote.gov/">Vote.gov</a> </li> </ul> </div> </div> </footer>  </div> </div> <script type="application/json" data-drupal-selector="drupal-settings-json">{"path":{"baseUrl":"\/","scriptPath":null,"pathPrefix":"","currentPath":"node\/411331","currentPathIsAdmin":false,"isFront":false,"currentLanguage":"en"},"pluralDelimiter":"\u0003","suppressDeprecationErrors":true,"back_to_top":{"back_to_top_button_trigger":100,"back_to_top_prevent_on_mobile":false,"back_to_top_prevent_in_admin":true,"back_to_top_button_type":"image","back_to_top_button_text":"Back to top"},"google_analytics":{"account":"G-HEQ0YF2VYL","trackOutbound":true,"trackMailto":true,"trackTel":true,"trackDownload":true,"trackDownloadExtensions":"7z|aac|arc|arj|asf|asx|avi|bin|bsh|c|csv|doc(x|m)?|dot(x|m)?|dw(fx|g|gd)|dxf|eps|epub|exe|f(90)|flv|gif|gz|gzip|hqx|jar|jpe?g|js|m1v|mp(2|3|4|e?g)|mobi|mov(ie)?|msi|msp|pdf|phps|pl|png|ppt(x|m)?|pot(x|m)?|pps(x|m)?|ppam|sld(x|m)?|thmx|qtm?|ra(m|r)?|rfa|rtf|rvt|sch|sea|sit|swf|tar|tgz|tif|txt|txz|wav|wma|wmv|wpd|wrl|xls(x|m|b)?|xlt(x|m)|xlam|xml|xsd|z|zip"},"nist_search":{"clickTracking":"search-report-click","isDebug":false,"clickTrackEnabled":true,"message":"NIST Search in debug mode. Check the browsers network inspector for Click Track reporting results..."},"data":{"extlink":{"extTarget":false,"extTargetNoOverride":false,"extNofollow":false,"extNoreferrer":false,"extFollowNoOverride":false,"extClass":"ext","extLabel":"(link is external)","extImgClass":false,"extSubdomains":true,"extExclude":"\\.gov\\\/|\\.mil\\\/|\\manufacturingusa\\.com\\\/","extInclude":"","extCssExclude":"","extCssExplicit":"","extAlert":true,"extAlertText":"Thank you for visiting NIST. We hope your visit was informative. We have provided a link to this site because it has information that may be of interest to our users. NIST does not necessarily endorse the views expressed or the facts presented on this site. Further, NIST does not endorse any commercial products that may be advertised or available on this site. Click OK to be directed to your link.","mailtoClass":"0","mailtoLabel":"(link sends email)","extUseFontAwesome":false,"extIconPlacement":"append","extFaLinkClasses":"fa fa-external-link","extFaMailtoClasses":"fa fa-envelope-o","whitelistedDomains":[]}},"user":{"uid":0,"permissionsHash":"2f77e4dcfce20728ac491170886da836c10b580f9bdfeb9c9e729fe4958834d5"}}</script> <script src="/web/20231209224628js_/https://www.nist.gov/sites/default/files/js/js_p8gamLXxPBoNiUHgUZaxT5BzySkZcDUazIUKuriGtWc.js?scope=footer&delta=0&language=en&theme=nist_www&include=eJx1kYGuwyAIRX_IVz_JUMuUzYoTXNe_X9utabPlJYbA4QZu0HNFe703rLPpwd-c8vKKPeXuKv-2yHM2gTkkdJAhzUpe7DcwmURdonwjdRdKitX-IhfgLRRSpLFUfqD9BquZjWnEERcPnHqobuTBDiTQL2vXoUZmURwXr4Kb3obEPaRz_vcZZSPCgHUv3TRNZ_WpXiX41HWBHWorkLpPaQpUCBVKlL1zkK7l0vpEEnEwD8JJ7Ba7xXVLaPzxBx1nj-ZCwUNR4rxf6yBvy3hvkFxEClEPlyP5yuuxXmYwua8"></script> <script src="https://web.archive.org/web/20231209224628js_/https://siteimproveanalytics.com/js/siteanalyze_6017546.js" async></script> <script src="/web/20231209224628js_/https://www.nist.gov/sites/default/files/js/js_Hd_E7OYn1o_yac29Cj8ar66acgtyWsIZ7h7tU5tKP24.js?scope=footer&delta=2&language=en&theme=nist_www&include=eJx1kYGuwyAIRX_IVz_JUMuUzYoTXNe_X9utabPlJYbA4QZu0HNFe703rLPpwd-c8vKKPeXuKv-2yHM2gTkkdJAhzUpe7DcwmURdonwjdRdKitX-IhfgLRRSpLFUfqD9BquZjWnEERcPnHqobuTBDiTQL2vXoUZmURwXr4Kb3obEPaRz_vcZZSPCgHUv3TRNZ_WpXiX41HWBHWorkLpPaQpUCBVKlL1zkK7l0vpEEnEwD8JJ7Ba7xXVLaPzxBx1nj-ZCwUNR4rxf6yBvy3hvkFxEClEPlyP5yuuxXmYwua8"></script> <script type="text/javascript">window.NREUM||(NREUM={});NREUM.info={"beacon":"gov-bam.nr-data.net","licenseKey":"37b7ccb661","applicationID":"1089704227","transactionName":"YFxUN0sADEdYVkBaClkWdwBNCA1aFkVVVABoWlcAUQQ=","queueTime":4,"applicationTime":42,"atts":"TBtXQQMaH0k=","errorBeacon":"gov-bam.nr-data.net","agent":""}</script></body> </html>

CINXE.COM

Time Realization and Distribution Group | NIST