Fundamental Physical Constants

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Mohr, David B. Newell, and Barry N. Taylor</strong><br>This database gives values of the basic constants and conversion factors of physics and chemistry resulting from the 2022 least-squares adjustment of the fundamental physical constants as published by the CODATA Task Group on Fundamental Constants and recommended for international use by CODATA.<br> </p><h2><a href="http://physics.nist.gov/cuu/Constants/Citations/Search.html">Searchable Bibliography of Fundamental Constants</a></h2><p><strong>Peter J. Mohr and Barry N. Taylor</strong><br>This searchable database gives the citations for the most important theoretical and experimental publications relevant to the fundamental physical constants and closely related precision measurements published since the mid 1980s. Earlier papers of particular interest are also included. The database is updated on a daily basis through the addition of papers from the current literature and made more comprehensive through the addition of earlier papers.<br> </p><h2><a href="/pml/owm/metric-si" data-entity-type="node" data-entity-uuid="d897ce5e-ca33-4ca5-b462-08c0e65c928c" data-entity-substitution="canonical" title="Metric (SI) Program">International System of Units (SI)</a></h2><p><strong>David B. Newell and Eite Tiesinga</strong><br>This is a description of the SI, the modern metric system of measurement. Long the language universally used in science, the SI has become the dominant language of international commerce and trade. Included are: 1) descriptions of base and derived SI units; 2) conversion factors from non-SI to SI units; and 3) rules and style conventions for spelling, printing, and using units of the SI (with SI prefixes), and for expressing values of quantities, including the results of measurements.<br> </p><h2><a href="https://www.nist.gov/pml/nist-technical-note-1297">Guidelines for Evaluating and Expressing Measurement Uncertainty</a></h2><p><strong>Barry N. Taylor and Chris E. Kuyatt</strong><br>This publication gives the NIST policy on expressing measurement uncertainty. Further, it succinctly summarizes the International Organization for Standardization (ISO) 100-page Guide to the Expression of Uncertainty in Measurement on which the NIST policy is based. Appendix D clarifies and gives additional guidance on a number of topics related to measurement uncertainty, including the use of certain terms such as accuracy and precision.<br> </p><h2><a href="https://uncertainty.nist.gov/">NIST Uncertainty Machine</a></h2> </div> </div> <div class="nist-block" >  <div data-elastic-exclude="" class="nist-tags"> <a href="/topic-terms/metrology" hreflang="en">Metrology</a>, <a href="/topic-terms/atomic-molecular-quantum" hreflang="en">Atomic / molecular / quantum</a>, <a href="/topic-terms/nuclear-physics" hreflang="en">Nuclear physics</a> and <a href="/topic-terms/reference-data" hreflang="en">Reference data</a></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"> <ul class="nist-contact__items"> <li class="nist-contact__item"> <div class="nist-contact__name"> PML webmaster </div> <div> <a href="mailto:pml-webmaster@nist.gov">pml-webmaster@nist.gov</a> </div> <div> </div> </li> </ul> </div> </div> <div class="nist-block" > <div class="text-italic font-sans-2xs"> Created June 10, 2009, Updated May 9, 2024 </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="/" title="National Institute of Standards and Technology" rel="home"> <img class="nist-footer__logo-img" src="/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="tel:301-975-2000">301-975-2000</a> </address> <p> <a href="mailto:do-webmaster@nist.gov">Webmaster</a> | <a href="https://www.nist.gov/about-nist/contact-us">Contact Us</a> | <a href="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--x-white" href=" https://x.com/NIST"> <span>X.com</span> </a> <a class="nist-social nist-social--facebook-white" href=" https://www.facebook.com/NIST"> <span>Facebook</span> </a> <a class="nist-social nist-social--linkedin-white" href=" https://www.linkedin.com/company/nist"> <span>LinkedIn</span> </a> <a class="nist-social nist-social--instagram-white" href=" https://www.instagram.com/nist/"> <span>Instagram</span> </a> <a class="nist-social nist-social--youtube-white" href=" https://www.youtube.com/NIST"> <span>YouTube</span> </a> <a class="nist-social nist-social--giphy-white" href=" https://giphy.com/nist"> <span>Giphy</span> </a> <a class="nist-social nist-social--rss-white" href=" https://www.nist.gov/news-events/nist-rss-feeds"> <span>RSS Feed</span> </a> <a class="nist-social nist-social--envelope-white" href=" https://public.govdelivery.com/accounts/USNIST/subscriber/new"> <span>Mailing List</span> </a> </div> <div class="nist-footer__feedback"> How are we doing? 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