  We have calibrated an extensive set of BVI observations of M67. We have
selected stars that are most likely to be single-star members of the cluster
using proper motion, radial velocity, and variability information from the
literature, and an examination of the most probable color-magnitude diagram
locations of unresolved stellar blends. Observations of M67 turnoff stars are a
severe test of algorithms attempting to describe convective cores in the limit
of small extent, and we find strong evidence of a ``hook'' just fainter than
the turnoff gap. The stars in M67 support assertions that the degree of
convective core overshooting decreases to zero for stars with masses in the
range 1.0 < (M / M_sun) < 1.5, but that the degree of overshoot is smaller than
currently used in published isochrones. We also verify that all current
theoretical models for the lower main sequence (with the exception of Baraffe
et al. 1998) are too blue for M_V >~ 6 even when the sequences are shifted to
match M67 near the M_V of the Sun, probably due to a combination of problems
with color-T_eff transformations and realistic surface boundary conditions for
models. Finally, we identify a subset of cluster members with unusual
photometry (candidate red giant binaries, blue straggler stars, and triple
systems) deserving of further study.
