Comparison of 0.3 (solid line), 1 (dashed), 3 (dotted), and 10 (dot-dashed) million-year isochrones for the cases ξ = 0.5, 0.1, 0.05, and 0 from top to bottom in the H-R diagram with observed PMS stars: ONC (red, small diamonds), ρ Oph (red squares), σ Ori (green circles), Tau-Aur (blue triangles), and Tau and Cha I (blue, inverted triangles). Each isochrone is comprised of evolutionary tracks of 0.01, 0.25, 0.05, 0.1, 0.3, 0.5, 0.8, and 1 M_⊙ stars denoted by pluses, crosses, asterisks, open squares, open circles, open triangles, open inverted triangles, and open tilted squares, respectively. The initial radius is 1.5 R_⊙ and X_D = 20 ppm. The isochrones with varying ξ cover the wide range of the region where the observed stars exist in the high-temperature regime.