  We compare theoretical stellar models for Main Sequence (MS) stars with the
Hipparcos database for the Hyades cluster to give a warning against the
uncritical use of available theoretical scenarios and to show how formal MS
fittings can be fortuitous if not fictitious. Moreover, we find that none of
the current theoretical scenarios appears able to account for an observed
mismatch between theoretical predictions and observations of the coolest Hyades
MS stars. Finally, we show that current theoretical models probably give too
faint He burning luminosities unlike the case of less massive He burning
models, with degenerate progenitors, which have been suggested to suffer the
opposite discrepancy.
