  We review the studies on the scaling of the minimal step-step distance lmin
in the bunch with the bunch size N, l_min~N^(-{\gamma}). We build our
retrospective around the different values of the exponent {\gamma} obtained
from models and experiments. It was mainly studied in the context of the
electromigration driven instability on Si(111) vicinal surfaces. In this
context the full scaling relation is given in general form as l_min ~
(A/l_cFN^2)^[1/(n+1)], where A is the magnitude of the step-step repulsions
with range n, F is the electromigration force acting on the charged surface
atoms and l_c is a length-scale, characteristic for the regime of step
bunching, diffusion-limited (DL) or attachment-detachment limited (KL).
