  The Calan/Tololo supernova survey has discovered ~30 Type Ia supernovae out
to z~0.1. Using BVI data for these objects and nearby SNe Ia, we have shown
that there exists a significant dispersion in the intrinsic luminosities of
these objects. We have devised a robust chisquare minimization technique
simultaneously fitting the BVI light curves to parametrize the SN event as a
function of (tb,m, m15(B)) where tb is the time of B maximum, m is the peak BVI
magnitude corrected for luminosity variations, and m15(B) is a single parameter
describing the whole light curve morphology. When properly corrected for
m15(B), SNe Ia prove to be high precision distance indicators,yielding relative
distances with errors 7-10%. The corrected peak magnitudes are used to
construct BVI Hubble diagrams (HD), and with Cepheid distances recently
measured with the HST to four nearby SNe Ia (37C, 72E, 81B, 90N) we derive a
value of the Hubble constant of 63.1+/-3.4 (internal) km/s/Mpc. This value is
~10-15% larger than the value obtained by assuming that SNe Ia are perfect
standard candles. As we have shown in Paper V, there is now strong evidence
that galaxies with younger stellar population appear to host the
slowest-declining, and therefore most luminous SNe Ia. Hence, the use of Pop I
objects such as Cepheids to calibrate the zero point of the SNe Ia HD can
easily bias the results toward luminous SNe Ia, unless the absolute
magnitude-decline relation is taken into account.
