  I argue that the laws of physics should be independent of one's choice of
units or measuring apparatus. This is the case if they are framed in terms of
dimensionless numbers such as the fine structure constant, alpha. For example,
the Standard Model of particle physics has 19 such dimensionless parameters
whose values all observers can agree on, irrespective of what clock, rulers,
scales... they use to measure them. Dimensional constants, on the other hand,
such as h, c, G, e, k..., are merely human constructs whose number and values
differ from one choice of units to the next. In this sense only dimensionless
constants are "fundamental". Similarly, the possible time variation of
dimensionless fundamental "constants" of nature is operationally well-defined
and a legitimate subject of physical enquiry. By contrast, the time variation
of dimensional constants such as c or G on which a good many (in my opinion,
confusing) papers have been written, is a unit-dependent phenomenon on which
different observers might disagree depending on their apparatus. All these
confusions disappear if one asks only unit-independent questions.
  We provide a selection of opposing opinions in the literature and respond
accordingly.
