We propose a zero-point photometric calibration of the data from the ACS/WFC on board the Hubble Space Telescope , based on a spectrum of Vega and the most up to date in-flight transmission curves of the camera .
This calibration is accurate at the level of a few hundredths of a magnitude .
The main purpose of this effort is to transform the entire set of evolutionary models by Pietrinferni et al .
( 2004 ) into a simple observational photometric system for ACS/WFC data , and make them available to the astronomical community .
We provide the zero points for the most used ACS/WFC bands , and give basic recipes for calibrating both the observed data and the models .

We also present the Colour Magnitude Diagram ( CMD ) from ACS data of 5 Galactic globular clusters , spanning the metallicity range -2.2 < [ Fe/H ] < -0.04 , and provide fiducial points representing their sequences from several magnitudes below the turnoff to the red giant branch tip .
The observed sequences are compared with the models in the newly defined photometric system .