  With this paper we continue the preparation for a forthcoming summary report
of our experiment with the Hubble Space Telescope (HST) to determine the Hubble
constant using type Ia supernovae as standard candles. Two problems are
addressed. (1) We examine the need for, and determine the value of, the
corrections to the apparent magnitudes of our program Cepheids in the eleven
previous calibration papers due to sensitivity drifts and charge transfer
effects of the HST WFPC2 camera over the life time of the experiment from 1992
to 2001. (2) The corrected apparent magnitudes are applied to all our previous
photometric data from which revised distance moduli are calculated for the
eight program galaxies that are parents to the calibrator Ia supernovae. Two
different Cepheid P-L relations are used; one for the Galaxy and one for the
LMC. These differ both in slope and zero-point at a fixed period. The
procedures for determining the absorption and reddening corrections for each
Cepheid are discussed. Corrections for the effects of metallicity differences
between the program galaxies and the two adopted P-L relations are derived and
applied. The distance moduli derived here for the eight supernovae program
galaxies, and for 29 others, average 0.20 mag fainter (more distant) than those
derived by Gibson et al. and Freedman et al. in their 2000 and 2001 summary
papers for reasons discussed in this paper. The effect on the Hubble constant
is the subject of our forthcoming summary paper.
