H-R diagrams for several PMS evolutionary models. Isochrones (dotted lines) correspond to 10 (top isochrone), 16, 25, 40, and 100 Myr (an additional 50 Myr isochrone is shown in the middle plot). Isomasses (continuous lines) are for 0.75 (bottom isomass), 0.80, 0.85, 0.90, 0.95, and 1.0 M_⊙. Points with error bars correspond to measurements (see Table 2). (Top) BCAH98 models, α = 1. (Middle) BCAH98 models, α = 1.9 (solar value). (Bottom) MDKH04 models.