  Hipparcos proper motions and trigonometric parallaxes allow the derivation of
secular parallaxes which fix the distances to individual stars in the Hyades
cluster to an accuracy of \sim 2 percent. The resulting color-absolute
magnitude diagram for 92 high-fidelity single members of the cluster displays a
very narrow main sequence, with two turn-offs and associated gaps. These occur
at the locations where the onset of surface convection affects the B-V colors,
as predicted by Boehm-Vitense thirty years ago. The new distances provide
stringent constraints on the transformations of colors and absolute magnitudes
to effective temperatures and luminosities, and on models of stellar interiors.
