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For the past two years, measurements have been performed with a watt balanceat the National Institute of Standards and Technology (NIST) to determine thePlanck constant. A detailed analysis of these measurements and theiruncertainties has led to the value $h=6.626\,069\,79(30)\times10^{-34}\,$J$\,$s. The relative standard uncertainty is $ 45\times 10^{-9}$.This result is $141\times 10^{-9}$ fractionally higher than $h_{90}$. Here$h_{90}$ is the conventional value of the Planck constant given by$h_{90}\equiv 4 /( K_{\mathrm{J-90}}^2R_{\mathrm{K-90}})$, where$K_{\mathrm{J-90}}$ and $R_{\mathrm{K-90}}$ denote the conventional values ofthe Josephson and von Klitzing constants, respectively.

Determination of the Planck constant using a watt balance with a superconducting magnet system at the National Institute of Standards and Technology