Left panel: Hertzsprung-Russell (HR) diagram showing the error stripe due to the variation of all the seven analyzed physical inputs (i.e. p₁,...,p₇ in Table 1) on the stellar track with M = 0.9 M_⊙, Z = 0.006, Y = 0.26 from pre-main sequence to helium flash. The narrowing of the error stripe in the RGB is due to the fact that the perturbed stellar models are disposed along the tracks itself. See text for details. Right panel: as in the left panel, but for the ZAHB.