M-T_eff-log g space from various view angles for main-sequence stars with solar initial composition. The red, blue, and green circles are the points taken from PARSEC, BaSTI, and DARTMOUTH isochrones or evolutionary tracks, respectively. The cyan surface with grids is the best surface fit to the theoretical PARSEC isochrones. The surface corresponds to the synthetic MTGR formula (see text). The solid black line represents the approximate position of the ZAMS.