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)× 10⁻³⁴\,J$\,$s. The relative standard uncertainty is 45× 10⁻⁹. This result is 141× 10⁻⁹ fractionally higher than h₉₀. Here h₉₀ is the conventional value of the Planck constant given by h₉₀≡ 4 /( KJ-90²RK-90), where KJ-90 and RK-90 denote the conventional values of the Josephson and von Klitzing constants, respectively.