The possible contribution of gravity measurements to the difference between the NIST and NRC watt balance results

We report on a 2012 comparison of gravity used to determine the Planck constant by the National Institute of Standards and Technology (NIST) and the National Research Council Canada (NRC) watt balances. The results provide verification of the gravity values used in recently published discrepant Planck constant determinations that play a vital role in the redefinition effort of the International System of Units (SI) and set an upper limit of 10 parts in 10 9 on the relative uncertainty contribution of gravity observations to future Planck constant determinations by the NIST and NRC watt balances.