  The MACHO Project is a microlensing survey that monitors the brightnesses of
60 million stars in the Large Magellanic Cloud (LMC), Small Magellanic Cloud,
and Galactic bulge. Our database presently contains about 80 billion
photometric measurements, a significant fraction of all astronomical
photometry. We describe the calibration of MACHO two-color photometry and
transformation to the standard Kron-Cousins V and R system. Calibrated MACHO
photometry may be properly compared with all other observations on the
Kron-Cousins standard system, enhancing the astrophysical value of these data.
For 9 million stars in the LMC bar, independent photometric measurements of
20,000 stars with V < 18 mag in field-overlap regions demonstrate an internal
precision sigV = 0.021, sigR = 0.019, and sig(V-R) = 0.028 mag. The accuracy of
the zero-point in this calibration is estimated to be +-0.035 mag for stars
with colors in the range -0.1 < (V-R) < 1.2 mag. A comparison of calibrated
MACHO photometry with published photometric sequences and new Hubble Space
Telescope observations shows agreement. The current calibration zero-point
uncertainty for the remainder of the MACHO photometry database is estimated to
be +- 0.10 mag in V or R and +-0.04 mag in (V-R). We describe the first
application of calibrated MACHO photometry data: the construction of a
color-magnitude diagram used to calculate our experimental sensitivity to
detect microlensing in the LMC.
