Relationship between the Rossby number, N_R, and the ratio of the surface flux of the chromospheric Ca II IRT emission line at 8542 Å to the stellar bolometric luminosity, R′. Circles represent PMS stars with narrow Ca II emission lines (<100 km s⁻¹), while squares represent PMS stars with broad Ca II emission lines (>100 km s⁻¹). Crosses denote ZAMS stars (Marsden et al. 2009; Yamashita & Itoh 2022). The color of the circles indicates the amount of veiling measured in 8420– 8560 Å.