Skip to main content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.


The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

A summary of the Planck constant measurements using a watt balance with a superconducting solenoid at NIST



Stephan Schlamminger, Richard L. Steiner, Darine El Haddad, David B. Newell, Frank C. Seifert, Leon S. Chao, Ruimin Liu, Edwin R. Williams


Researchers at the National Institute of Standards and Technology have been using a watt balance, NIST-3, to measure the Planck constant h for over ten years. Two recently published values disagree by more than one standard deviation. The motivation for the present manuscript is twofold. First, we correct the latest published number to take into account a recently discovered systematic error in mass dissemination at the Bureau International des Poids et Mesures (BIPM). Second, we provide guidance on how to combine the two numbers into one final result. In order to adequately reflect the discrepancy, an additional systematic uncertainty must be added to the published error budgets. The final value of h measured with NIST-3 is h = 6.626 069 36(37) x 10^-34 Js. This result is 77(57) x 10^-9 fractionally higher than h_90. Here, h_90 is the conventional value of the Planck constant given by h_90~ 4 /(KJn^2 RKn), where KJn and RKn denote the conventional values of the Josephson and von Klitzing constants, respectively.


watt balance, electronic kilogram, Planck constant
Created February 5, 2015, Updated November 10, 2018