HR diagrams of tracks computed with Z = 10⁻¹¹, Z = 0.001 and Z = 0.014, in the left-hand, center, and right-hand panels, respectively. Tracks are shown beginning from the ZAMS, indicated by the dashed red line. The dash-dotted black line indicates the TAMS. Blue dots (crosses) indicate the beginning (end) of core helium-burning, respectively. Pink stars indicate the final position of the star. The pre-MS phase is not shown for clarity. The stellar mass in solar masses of some selected tracks indicated by the solid green lines is written near their corresponding ZAMS position. Diagonal dashed gray lines show constant stellar radii as labeled.