Interpolated evolutionary tracks (red lines) from the original theoretical set of evolutionary tracks (blue lines). Upper panel: metallicity interpolation (metallicity increases from left to right) with constant helium abundance Y = 0.245 and mass of 0.9 M_⊙. Middle panel: helium interpolation (helium increases from right to left) with constant metallicity Z = 0.0016 and masses of 0.9 (hotter) and 0.5 M_⊙ (cooler). Bottom panel: mass interpolation (mass increases from right to left) with constant metallicity Z = 0.0016 and helium abundance Y = 0.245.