Measurement of the Planck constant at the National Institute of Standards and Technology from 2015 to 2017
  Researchers at the National Institute of Standards and Technology(NIST) have
measured the value of the Planck constant to be $h =6.626\,069\,934(89)\times
10^{-34}\,$J$\,$s (relative standard uncertainty $13\times 10^{-9}$). The
result is based on over 10$\,$000 weighings of masses with nominal values
ranging from 0.5$\,$kg to 2$\,$kg with the Kibble balance NIST-4. The
uncertainty has been reduced by more than twofold relative to a previous
determination because of three factors: (1) a much larger data set than
previously available, allowing a more realistic, and smaller, Type A
evaluation; (2) a more comprehensive measurement of the back action of the
weighing current on the magnet by weighing masses up to 2$\,$kg, decreasing the
uncertainty associated with magnet non-linearity; (3) a rigorous investigation
of the dependence of the geometric factor on the coil velocity reducing the
uncertainty assigned to time-dependent leakage of current in the coil.
