  We provide an overview of the fundamental units of physical quantities
determined naturally by the values of fundamental constants of nature. We
discuss a comparison between the 'Planck units', now widely used in theoretical
physics and the pre-quantum 'Stoney units' in which, instead of the Planck
constant, the charge of the electron is used with very similar quantitative
results. We discuss some of the physical motivation for these special units,
attributed much after they were introduced, and also put forth a summary of the
arguments supporting various cases for making specific physical interpretations
of the meanings of some of these units. The new aspects we discuss are a
possible physical basis for the Stoney units, their link to the Planck units,
and also the importance of Planck units for thermodynamical quantities in the
context of quantum gravity.
