coverage [@Grillmair95; @LS97 for works on this subject], allows us to go deeper inside the core of the clusters, to better handle photometric errors and completeness corrections and to reach a considerably fainter magnitude level. CCDs also allows in the case of high concentration clusters to complement star counts of the central part with aperture photometry of short exposures images [@Ivo97].

An important byproduct of this study is the photometry of a significant number of stars in all the principal sectors of the CMD. This sample is of fundamental importance to test modern evolutionary stellar models [@RFP88]. In all cases the CMD extends well below the turn off of the main sequence. This permits us to estimate the effect of mass segregation for masses from the TO mass ($\sim0.8\Msun$) down to $0.6, 0.5\Msun$.

So far, we have collected data for a total of 19 clusters. Same of them have already been reduced and analyzed. In this work we present the analysis of the star counts of the globular cluster =M55. Other clusters, for which we have already given a first report elsewhere [@Zaggia95; @Carla96; @Ivo95; @Alf96], will be presented in future works [@Ivo97; @Alf97].

Why the globular cluster M55?
=============================

