M3 according to the difference of $E(B-V)$ values and distance moduli (see Sections 3.2, 3.3 and 3.4 for details about the values adopted). As apparent from the upper panels of Figure \[m13m79\] and \[m13m3\], once relative differences in reddening and distance are taken into account, the CMDs match well at the TO level and along the RGB, consistently with the fact that they have almost the same age and share a similar metallicity.\
In the bottom panels we focus on their Turn Off (TO) region. Also from a close inspection, the CMDs have been found to nicely overlap at the TO and SGB region. This already rules out any significant age difference between M13, M3 and M79. However in order to perform a more accurate comparison, we also used two isochrones of proper metallicity and different age from the BaSTI database (Pietrinferni et al. 2006). In particular we used as reference the isochrone that best fits the observed CMD ($t=12$ Gyr) and an additional one that is $1.5$ Gyr older[^5]. As apparent from the left bottom panels of Figures \[m13m79\] and \[m13m3\], the older isochrone does not match either the TO or the SGB.\
Starting from these isochrones, and using 