NOTICE: Due to a lapse in annual appropriations, most of this website is not being updated. Learn more.

Form submissions will still be accepted but will not receive responses at this time. Sections of this site for programs using non-appropriated funds (such as NVLAP) or those that are excepted from the shutdown (such as CHIPS and NVD) will continue to be updated.

U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

PUBLICATIONS

An Accurate Measurement of Planck's Constant

Published

Author(s)

Edwin R. Williams, Richard L. Steiner, David B. Newell

Abstract

Using a moving coil watt balance, electric power measured in terms of the Josephson and quantum Hall effects is compared with mechanical power measured in terms of the meter, kilogram and second, we find the Planck constant h = 6.62606891(58) x 10-34 Js. The quoted standard uncertainty ( 1 standard deviation estimate) corresponds to (8.7 x 10-8) h. Comparing this measurement places an upper limit of 2 x 10-8 / year on the drift rate of the SI unit of mass, the Kilogram.
Citation
Physical Review Letters
Pub Type
Journals

Keywords

electron mass, fundamental constants, Josephson constants, kilogram, mass drift, Planck constant, Watt-SI

Citation

Williams, E. , Steiner, R. and Newell, D. (1998), An Accurate Measurement of Planck's Constant, Physical Review Letters (Accessed November 5, 2025)

Issues

If you have any questions about this publication or are having problems accessing it, please contact [email protected].

Created June 30, 1998, Updated October 12, 2021
Was this page helpful?