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The NRC Kibble Balance, Final Measurements of h

PTB Kolloquium

It seems almost inevitable that this November the General Conference on Weights and Measures (CGPM) will approve the redefinition of the SI, our system of units. This process has taken over a decade of metrological negotiations, accompanied by an intense effort to improve measurements of the values of the Planck, Avogadro and Boltzmann constants.

I will very briefly outline the Revised SI and describe the two techniques that are competitive for determining values for the Avogadro and Planck constants at the highest accuracy. The bulk of the talk will focus on the NRC Kibble balance and its determination of the value of h. In particular, a number of innovations that are critical or unique to the NRC determinations of Planck’s constant will be described. Finally, I will talk about the how the CODATA Task Group on Fundamental Constants performed a special adjustment of the fundamental constants with the purpose of setting the fixed values of the reference constants of the revised SI.