  Atoms and molecules can serve as sensitive probes of a possible variation of
the fine structure constant $\alpha$ and electron-to-proton mass ratio $\mu$.
Two types of sensitivity coefficients are often used to quantify and compare
the sensitivity of different species to the variation of fundamental constants.
The dimensionless coefficients $K$ are related to the fractional sensitivity,
while dimensional factors $q$ are related to the absolute sensitivity. Here we
discuss several common errors and misconceptions regarding these coefficients
that frequently appear in the literature.
