  We discuss the least-square and linear-regression methods, which are relevant
for a reliable determination of good nuclear-mass-model parameter sets and
their errors. In this perspective, we define exact and inaccurate models and
point out differences in using the standard error analyses for them. As an
illustration, we use simple analytic models for nuclear binding energies and
study the validity and errors of models' parameters, and uncertainties of its
mass predictions. In particular, we show explicitly the influence of
mass-number dependent weights on uncertainties of liquid-drop global
parameters.
