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http-equiv="X-UA-Compatible" content="IE=8"/> <title>BIPM - Time </title> <meta name="description" content="Time "> <script language="javascript" src="/web/20200202204857js_/https://www.bipm.org/utils/onLoad.js"> </script> <script> (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){ (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o), m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m) })(window,document,'script','//web.archive.org/web/20200202204857/https://www.google-analytics.com/analytics.js','ga'); ga('create', 'UA-38070491-1', 'auto'); ga('send', 'pageview'); </script> <script src="/web/20200202204857js_/https://www.bipm.org/utils/jquery/jquery-1.10.2.min.js"></script> <script src="/web/20200202204857js_/https://www.bipm.org/utils/jquery/jquery-ui-1.10.3.custom/js/jquery-ui-1.10.3.custom.js"></script> <script src="/web/20200202204857js_/https://www.bipm.org/utils/zee/unslider.min.js"></script> <script 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<td width="10"><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img/pix.gif" width="10" height="90"></td> <td width="180" valign="center" align="left"><a href="/web/20200202204857/https://www.bipm.org/en/about-us/" title="BIPM home page"><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img/logoBIPM-RB.jpg" border="0"></a></td> <td width="530" valign="center" align="center" class="intro">    the intergovernmental organization through which Member States act together<br>      on matters related to measurement science and measurement standards.</td> <td width="270" align="center" valign="top"> <script language="javascript"> function ActionForm(f) { f.q.style.background = "white"; } </script> <form name="search" action="https://web.archive.org/web/20200202204857/https://search.bipm.org/bipm/en/C="> <table width="180" align="right" valign="top" border="0"> <tr height="50"> <td valign="bottom" class="intro">Search facility: <input 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href="/web/20200202204857/https://www.bipm.org/en/measurement-units/base-units.html" target="_self">Unit definitions</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/measurement-units/prefixes.html" target="_self">SI prefixes</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/si-download-area/" target="_self">Revised SI: Download area</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/measurement-units/history-si/" target="_self">Brief history of the SI</a></li> </ul> </li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm-services/" target="_self"> Services</a> <ul> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm-services/comparisons/" target="_self">Comparisons piloted by the BIPM</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm-services/calibrations/" target="_self">Calibration and measurement services</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/tai/" target="_self">Timescales</a></li> <li><a href="https://web.archive.org/web/20200202204857/https://www.bipm.org/kcdb" target="_self"><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img2/logo_kcdb_pt.gif" alt="KCDB" vspace="2"></a></li> <li><a href="https://web.archive.org/web/20200202204857/https://www.bipm.org/jctlm/" target="_self"><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img2/logo_jctlm_pt.gif" alt="JCTLM" vspace="2"></a></li> <li><a href="https://web.archive.org/web/20200202204857/http://imrr.bipm.org/" target="_self"><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img2/logo_imrr_pt.gif" alt="IMRR" vspace="2"></a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/si-brochure/" target="_self">SI Brochure</a></li> <li><a href="https://web.archive.org/web/20200202204857/http://iopscience.iop.org/0026-1394/" target="metrologia"><i>Metrologia</i></a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/conference-centre/" target="_self">Meetings</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/mises-en-pratique/standard-frequencies.html" target="_self">Recommended values of standard frequencies</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/ionizing/radionuclides/sir/" target="_self">International Reference System (SIR)</a></li> </ul> </li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/" target="_self"> Publications</a> <ul> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/si-brochure/" target="_self">SI Brochure</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/mises-en-pratique/" target="_self"><i>Mises en pratique</i></a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/directors-report/" target="_self">Annual Director's Report</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/committees/cipm/publications-cipm.html#ra" target="_self">Financial Report</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/committees/cipm/publications-cipm.html#no" target="_self">Notification of Contributions</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/" target="_self">Official proceedings</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/worldwide-metrology/cgpm/resolutions.html" target="_self">Resolutions of the General Conference</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/open-literature/" target="_self">Scientific output</a></li> <li><a href="https://web.archive.org/web/20200202204857/http://iopscience.iop.org/0026-1394/" target="metrologia"><i>Metrologia</i></a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/guides/" target="_self">Guides in Metrology</a></li> </ul> </li> <li><a href="/web/20200202204857/https://www.bipm.org/en/conference-centre/diary/" target="_self"> Meetings</a> <ul> <li><a href="/web/20200202204857/https://www.bipm.org/en/conference-centre/diary/" target="_self">List of meetings</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/conference-centre/" target="_self">BIPM Conference Centre</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/conference-centre/directions/" target="_self">How to get to the BIPM</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/cgpm-2018/" target="_self">General Conference (CGPM)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/committees/cipm/" target="_self">International Committee (CIPM)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/committees/cc/" target="_self">Consultative Committees and Working Groups</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/conference-centre/bipm-workshops/" target="_self">BIPM Workshops</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/conference-centre/other-events/" target="_self">Other BIPM events</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/" target="_self">Meeting reports</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/worldwide-metrology/metrology-events.html" target="_self">External events</a></li> </ul> </li> </ul> </div> </td> </tr> </table>   <table width="1000" height="25" border="0" cellspacing="0" cellpadding="0"> <tr height="25"> <td height="25" bgcolor="#DBE3EB"> <table width="100%" border="0" cellspacing="0" cellpadding="0"> <tr> <td width="10"><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img/pix.gif" width="10"></td> <td class="navigation" width="100%">> You are here: <a href="/web/20200202204857/https://www.bipm.org/en/bipm/" class="navigation">BIPM work programme</a> > Time </td> <td width="10"><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img/pix.gif" width="10"></td> </tr> </table> </td> </tr> </table>   <center> <table width="1000" border="0" cellspacing="0" cellpadding="0"> <tr> <td width="10" height="50"><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img/pix.gif" width="10" height="50"></td> <td align="left" width="100%" height="50" background="/web/20200202204857im_/https://www.bipm.org/utils/common/img/cadre_trait.gif"> <table width="100%" border="0" background="/web/20200202204857im_/https://www.bipm.org/en/bipm/tai/"> <tr> <td align="left" class="GrosTitre"><div name="exalead-titre">Time </div></td> </tr> </table> </td> <td width="10" height="50"><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img/pix.gif" width="10" height="50"></td> </tr> </table> </center>  <center> <table width="1000" border="0" cellspacing="0" cellpadding="0"> <tr height="5"><td colspan="3"></td></tr> <tr valign="top"> <td width="10"><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img/pix.gif" width="10"></td> <td width="100%" class="txt12pt"> <div id="tabs"> <ul> <li><a href="#overview">Overview</a></li> <li><a href="#"><a href="/web/20200202204857/https://www.bipm.org/en/bipm/tai/timescale-generation/">International reference time scales</a></a></li> <li><a href="#"><a href="/web/20200202204857/https://www.bipm.org/en/bipm/tai/circular-t/">TAI and UTC: <i>Circular T</i>  </a></a></li> <li><a href="#"><a href="/web/20200202204857/https://www.bipm.org/en/bipm/tai/utcr/">Rapid UTC (UTCr)  </a></a></li> <li><a href="#"><a href="/web/20200202204857/https://www.bipm.org/en/bipm/tai/ttbipm/">TT(BIPM)</a></a></li> <li><a href="#"><a href="/web/20200202204857/https://www.bipm.org/en/bipm/tai/time-transfer/">Time transfer</a></a></li> <li><a href="#"><a href="/web/20200202204857/https://www.bipm.org/en/bipm/tai/time-services/">Time services</a></a></li> <li><a href="#"><a href="/web/20200202204857/https://www.bipm.org/en/bipm/tai/time-publications/">Time publications</a></a></li> <li><a href="#"><a href="/web/20200202204857/https://www.bipm.org/en/bipm/tai/coordination-work/">International cooperation and coordination</a></a></li> <li><a href="#link"><a href="https://web.archive.org/web/20200202204857/http://webtai.bipm.org/database/html/">Time Department Database</a></a></li> <li><a href="#Staff of the BIPM Time Department"><a href="members.html">Staff of the BIPM Time Department</a></a></li> </ul> <div id="overview"> <div name="exalead">  <center> <table width="90%" bgcolor="#829EBA" cellpadding="20" cellspacing="3" border="0"> <tr> <td valign="top"> <table cellpadding="12" cellspacing="5"> <tr><td bgcolor="#FFFFFF" class="upMenu"><a href="/web/20200202204857/https://www.bipm.org/en/bipm-services/timescales/" class="introGras"><nobr><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img/flc_dir_bleu.gif"> Timescales</nobr></a></td></tr> <tr><td bgcolor="#FFFFFF" class="upMenu"><nobr><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img/flc_dir_bleu.gif"> <a href="https://web.archive.org/web/20200202204857/http://webtai.bipm.org/database/html/" class="introGras">Database</a></nobr></td></tr> <tr><td bgcolor="#FFFFFF" class="upMenu"><nobr><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img/flc_dir_bleu.gif"> <a href="/web/20200202204857/https://www.bipm.org/en/bipm-services/timescales/time-ftp.html" class="introGras">FTP server</a></nobr></td></tr> </table> </td> <td bgcolor="#FFFFFF"> <p class="SousTitre"><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img/fleche_jaune.gif" width="29" height="14" alt="">Key products of the BIPM Time Department:</p> <ul class="txt12pt"> <li>The <a href="/web/20200202204857/https://www.bipm.org/en/bipm-services/timescales/time-ftp/cirt.html" class="introGras">atomic time scales TAI and UTC</a> are disseminated monthly through the <a href="/web/20200202204857/https://www.bipm.org/en/bipm-services/timescales/time-ftp/Circular-T.html" class="introGras">BIPM <i>Circular T</i></a>.</li> <br> <li>A <a href="/web/20200202204857/https://www.bipm.org/en/bipm-services/timescales/time-ftp/Rapid-UTC.html" class="introGras">rapid solution of UTC (UTCr)</a> is published weekly, and allows participating national institutes to monitor the steering of their local realizations of UTC at shorter intervals than the monthly <i>Circular T</i>.</li> <br> <li>The <a href="annual-report.html" class="introGras"><i>BIPM Annual Report on Time Activities</i></a> provides all relevant information, data and results for the year previous to its publication.</li><br><li>Reports on time-transfer techniques are also issued regularly.</li> <br> <li>Other activities related to the time scales are developed in the Department; these contribute to improving the calculation algorithms and increasing knowledge about time transfer techniques. Coordination with the national time laboratories contributing data to UTC, and with international organizations acting on fields related to time keeping and regulations represent a significant part of the Time Department activities.</li></ul> <center> <table width="400" bgcolor="#829EBA" cellpadding="20" cellspacing="3"> <tr><td bgcolor="#F2F5F8"> <ul> <li><a href="/web/20200202204857/https://www.bipm.org/utils/en/pdf/BIPM-Work-Programme_2016-2019_TAI.pdf" class="introGras">BIPM Work Programme 2016-2019: Time <img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img/pdf.gif" border="0" alt=""></a></li> <li><a href="https://web.archive.org/web/20200202204857/http://stacks.iop.org/0026-1394/56/015020" class="introGras" target="_blank">News from the BIPM laboratories  2018</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/directors-report/" class="introGras">Director's Report</a></li> <li>Detailed reports on the Time Department: <ul><a href="/web/20200202204857/https://www.bipm.org/utils/common/pdf/DIR/DIR2017/time2017.pdf" class="intro">2017</a> | <a href="/web/20200202204857/https://www.bipm.org/utils/common/pdf/DIR/DIR2016/time2016.pdf" class="intro">2016</a> | <a href="/web/20200202204857/https://www.bipm.org/utils/common/pdf/DIR/DIR2015/time2015.pdf" class="intro">2015</a> | <a href="/web/20200202204857/https://www.bipm.org/utils/common/pdf/DIR/DIR2014/time2014.pdf" class="intro">2014</a> | <a href="/web/20200202204857/https://www.bipm.org/utils/common/pdf/DIR/DIR2013/time2013.pdf" class="intro">2013</a></ul></li> <li><a href="annual-report.html" class="introGras">Annual Report on Time Activities</a></li> </ul> </td></tr></table> </center> </td> </tr> </table> </center> <p><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img/fleche_jaune.gif" width="29" height="14" alt="">The realization and dissemination of the international time scales is the responsibility of the BIPM Time Department.</p> <ul><li>International Atomic Time (TAI) is the uniform time scale; its unit interval is kept as close as possible to the <a href="/web/20200202204857/https://www.bipm.org/en/metrology/time-frequency/units.html" class="introGras">SI second</a>.</li><br> <li>Coordinated Universal Time (UTC) is an atomic time scale derived from TAI, to provide a reference scale in step with the irregular rotation of the Earth.</li></ul> <p>Local realizations of UTC exist at the <a href="https://web.archive.org/web/20200202204857/ftp://ftp2.bipm.org/pub/tai/publication/acronyms/acronyms.pdf" class="introGras">national time laboratories</a>. These laboratories participate in the calculation of the international time scales by sending their clock data to the BIPM. Most of them are equipped with commercial caesium beams that provide a practical realization of the second sufficiently accurate for most applications. More accurate caesium standards exist in a small number of laboratories; for them, the uncertainties are estimated to be a few parts in 10<sup>16</sup>. New developments in clocks using trapped or cooled atoms or ions are leading to improvements well beyond this. Progress in the construction of optical clocks represents a potential approach to 10<sup>18</sup> accuracy in a few years, and opens the way to a redefinition of the second.</p>  </div> </div> </div> </td> <td width="10"><img src="/web/20200202204857im_/https://www.bipm.org/utils/common/img/pix.gif" width="10"></td> </tr> <tr height="5"><td colspan="3"></td></tr> </table> </center>   <table width="100%" bgcolor="#D3B657"> <tr> <td width="15%"></td> <td width="1000"> <table width="1000" border="0" cellspacing="0" cellpadding="0"> <tr> <td nowrap width="100%"> <style media="all" type="text/css"></style> <div class="menu3"> <ul> <li><a href="/web/20200202204857/https://www.bipm.org/en/worldwide-metrology/" target="_self">Metrology area:</a></li> <li><a id="" href="/web/20200202204857/https://www.bipm.org/metrology/auv/" target="_self">AUV</a> <ul> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/auv/" target="_self">Metrology in the field of Acoustics, Ultrasound and Vibration</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/committees/cc/ccauv/" target="_self">Committee structure (CCAUV)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/auv/#strategy" target="_self">Strategic plan</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/si-brochure/" target="_self">Units (SI Brochure)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/people/gpanfilo.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200202204857/https://www.bipm.org/metrology/electricity-magnetism/" target="_self">EM</a> <ul> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/electricity-magnetism/" target="_self">Metrology in the field of Electricity and Magnetism</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/committees/cc/ccem/" target="_self">Committee structure (CCEM)</a></li> <li><a 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</ul> </li> <li><a id="" href="/web/20200202204857/https://www.bipm.org/metrology/length/" target="_self">L</a> <ul> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/length/" target="_self">Length Metrology</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/committees/cc/ccl/" target="_self">Committee structure (CCL)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/length/#strategy" target="_self">Strategic plan</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/length/units.html" target="_self">Unit of length (metre)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/mises-en-pratique/standard-frequencies.html" target="_self">Recommended values of standard frequencies</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/people/gpanfilo.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200202204857/https://www.bipm.org/metrology/mass/" target="_self">M</a> <ul> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/mass/" target="_self">Mass Metrology</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/committees/cc/ccm/" target="_self">Committee structure (CCM)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/mass/#strategy" target="_self">Strategic plan</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/mass/units.html" target="_self">Unit of mass (kilogram)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/mass/" target="_self">BIPM laboratory work</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/mass/calibrations_mass/" target="_self">Calibration services</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/mass/publications.html" target="_self">BIPM publications in the scientific literature</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/mass/contact.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200202204857/https://www.bipm.org/metrology/photometry-radiometry/" target="_self">PR</a> <ul> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/photometry-radiometry/" target="_self">Metrology in the field of Photometry and Radiometry</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/committees/cc/ccpr/" target="_self">Committee structure (CCPR)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/utils/en/pdf/CCPR-strategy-document.pdf" target="_self">Strategic plan</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/photometry-radiometry/units.html" target="_self">Photometric units</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/photometry-radiometry/liaisons.html" target="_self">BIPM liaison and coordination work</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/people/jviallon.html" target="_self">BIPM 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href="/web/20200202204857/https://www.bipm.org/en/bipm-services/calibrations/#chemistry" target="_self">BIPM calibrations: National ozone standards</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/chemistry-biology/publications.html" target="_self">BIPM publications in the scientific literature</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/chemistry-biology/liaisons.html" target="_self">BIPM liaison and coordination work</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/people/rwielgosz.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200202204857/https://www.bipm.org/metrology/ionizing-radiation/" target="_self">RI</a> <ul> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/ionizing-radiation/" target="_self">Metrology in the field of Ionizing Radiation</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/committees/cc/ccri/" target="_self">Committee structure (CCRI)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/ionizing-radiation/#strategy" target="_self">Strategic plan</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/ionizing-radiation/units.html" target="_self">SI units</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/ionizing/radionuclides/sir/" target="_self">International Reference System (SIR)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/ionizing/" target="_self">BIPM laboratory work</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm-services/comparisons/#RI" target="_self">Ongoing BIPM comparisons</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm-services/calibrations/#ionizing-radiation" target="_self">BIPM calibrations: Ionization chambers</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/ionizing-radiation/publications.html" target="_self">BIPM publications in the scientific literature</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/scientific-output/monographies-ri.html" target="_self"><i>Monographies</i> BIPM</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/ionizing-radiation/liaisons.html" target="_self">BIPM liaison and coordination work</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/people/steven.judge.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200202204857/https://www.bipm.org/metrology/thermometry/" target="_self">T</a> <ul> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/thermometry/" target="_self">Metrology in Thermometry</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/committees/cc/cct/" target="_self">Committee structure (CCT)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/thermometry/#strategy" target="_self">Strategic plan</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/thermometry/units.html" target="_self">SI base unit (kelvin)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/people/susanne.picard.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200202204857/https://www.bipm.org/metrology/time-frequency/" target="_self">TF</a> <ul> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/time-frequency/" target="_self">Time and Frequency Metrology</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/committees/cc/cctf/" target="_self">Committee structure (CCTF)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/time-frequency/#strategy" target="_self">Strategic plan</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm-services/timescales/time-server.html" target="_self">What time is it?</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm-services/timescales/" target="_self">Timescales</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/time-frequency/units.html" target="_self">Unit of time (second)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/mises-en-pratique/standard-frequencies.html" target="_self">Recommended values of standard frequencies</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/tai/" target="_self">BIPM technical work</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/jsp/en/TimeCalibrations.jsp" target="_self">BIPM calibrations for time transfer</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/time-frequency/publications.html" target="_self">BIPM technical publications</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/tai/annual-report.html" target="_self">BIPM Annual Report on Time Activities</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm-services/timescales/time-ftp.html" target="_self">FTP server of the BIPM Time Department</a></li> <li><a href="https://web.archive.org/web/20200202204857/http://webtai.bipm.org/database/html/" target="_self">Time Department Database</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/metrology/time-frequency/liaisons.html" target="_self">BIPM liaison and coordination work</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/bipm/people/patrizia.tavella.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200202204857/https://www.bipm.org/en/measurement-units/" target="_self">U</a> <ul> <li><a href="/web/20200202204857/https://www.bipm.org/en/measurement-units/" target="_self">Measurement units: the International System (SI)</a></li> <li><a href="/web/20200202204857/https://www.bipm.org/en/publications/si-brochure/" target="_self">SI Brochure</a></li> <li><a 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