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

For the past two years, measurements have been performed with a watt balance at the National Institute of Standards and Technology (NIST) to determine the Planck constant. A detailed analysis of these measurements and their uncertainties has led to the value $h=6.626,069,79(30)\times 10^{-34},$J$,$s\mathrm{.}Therelativestandarduncertaintyis$ 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 $h_{90}\equiv 4\mathrm{/}(K_{\mathrm{J}-90}^2{R}_{\mathrm{K}-90})$, where $K_{\mathrm{J}-90}$ and $R_{\mathrm{K}-90}$ denote the conventional values of the Josephson and von Klitzing constants, respectively.