A global effort to redefine our International System of Units (SI) is underway, and the change
to the new system is expected to occur in 2018. Within the newly redefined SI, the present
base units will still exist but be derived from fixed numerical values of seven reference
constants. In particular, the unit of mass (the kilogram) will be realized through a fixed value
of the Planck constant h. A so-called watt balance, for example, can then be used to realize
the kilogram unit of mass within a few parts in 10 8. Such a balance has been designed and …