Hα equivalent width and excess Hα equivalent width as functions of effective temperature. Panel (a) shows EW_Hα for RS CVn systems, with points color coded by surface gravity and the red curve indicating the empirical inactive baseline. Panel (b) shows ﹩{\rm{EW}}{{\prime} }_{{\rm{H}}\alpha }﹩ for the same RS CVn sample; color represents the local number of measurements, the black points and line show the binned medians, and the dashed horizontal line marks ﹩{{\rm{EW}}}_{{\rm{H}}\alpha }^{{\prime} }=0﹩. Panel (c) shows EW_Hα for other MS eruptive stars with the same inactive baseline, and panel (d) shows the corresponding ﹩{\rm{EW}}{{\prime} }_{{\rm{H}}\alpha }﹩ distribution and binned medians. The inactive sequence is constructed at the independent-source level using 100 K bins, a minimum of 10 sources per bin, the 10th percentile below 4000 K, and the 15th percentile at higher temperatures.