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The NIST Watt Balance: Recent Results and Future Plans



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


The last remaining SI base unit defined by an artifact is the kilogram. The NIST watt balance has been designed to measure the ratio of mechanical to electrical power, linking the artifact kilogram, the meter, and the second to the practical realizations of the ohm and the volt derived from the quantum Hall effect and the Josephson effect. Our recent results1 set an upper limit of 2 x 10-8/yr on the drift rate of the kilogram. By assuming the Josephson and von Klitzing effects are exact, we also determine the Planck constant h = 6.62606891(58) x 10-34 Js. Modifications to the experiment and facilities are being made to achieve the next goal: providing an alternative kilogram definition in terms of fundamental constants.
Bulletin of the American Physical Society


fundamental constant, kilogram, mass drift, planck's constant


Newell, D. , Steiner, R. and Williams, E. (1999), The NIST Watt Balance: Recent Results and Future Plans, Bulletin of the American Physical Society (Accessed April 18, 2024)
Created March 1, 1999, Updated October 12, 2021