The NRC is showing that by comparing two physical constants (Planck and ampere ) any lab will have an accurate measure of the kilogram.
if the SI were to be redefined, fixing the value of the Planck constant, the watt balance would provide a mechanism whereby any suitably equipped laboratory could determine the unit of mass; placing mass on the same footing within the SI as length and time. The redefinition process cannot be rushed as this change must be made in a manner that does not affect worldwide measurements of mass, and
http://www.npl.co.uk/engineering-measurements/mass-force-pressure/mass/research/npl-watt-balance
