  Newly acquired data and improved data reduction algorithms mandate a fresh
look at the absolute flux calibration of the CCD cameras on the Hubble Space
Telescope (HST) Advanced Camera for Surveys (ACS). The goals are to achieve a
1\% accuracy and to make this calibration more accessible to the HST guest
investigator. Absolute fluxes from the
CALSPEC\footnote{http://www.stsci.edu/hst/observatory/crds/calspec.html}
database for three primary hot 30,000--60,000K WDs define the sensitivity
calibrations for the WFC and HRC filters. The external uncertainty for the
absolute flux is $\sim$1\%, while the internal consistency of the sensitivities
in the broadband ACS filters is $\sim$0.3\% among the three primary WD flux
standards. For stars as cool as K type, the agreement with the CALSPEC
standards is within 1\% at the WFC1-1K subarray position, which achieves the
1\% precision goal for the first time. After making a small adjustment to the
filter bandpass for F814W, the 1\% precision goal is achieved over the full
F814W WFC field of view for stars of K type and hotter. New encircled energies
and absolute sensitivities replace the seminal results of Sirianni et al. that
were published in 2005. After implementing the throughput updates, synthetic
predictions of the WFC and HRC count rates for the average of the three primary
WD standard stars agree with the observations to 0.1\%.
