  For more than three decades, measurement of terrace width distributions
(TWDs) of vicinal crystal surfaces have been recognized as arguably the best
way to determine the dimensionless strength $\tilde{A}$ of the elastic
repulsion between steps. For sufficiently strong repulsions, the TWD is
expected to be Gaussian, with $\tilde{A}$ varying inversely with the squared
variance. However, there has been a controversy over the proportionality
constant. From another perspective the TWD can be described as a continuous
generalized Wigner distribution (CGWD) essentially no more complicated than a
Gaussian but a much better approximation at the few calibration points where
exact solutions exist. This paper combines concisely the experimentally most
useful results from several earlier papers on this subject and describes some
advancements that are in progress regarding numerical tests and in using
Schr\"odinger-equation formalism to give greater understanding of the origin of
the CGWD and to give hope of extensions to more general interaction potentials
between steps. There are many implications for future experiments.
