Spectral types vs. EW(CaT) for 185 known Galactic RSGs, with their EW(CaT) measurements from Cesetti et al. (2013), Dorda et al. (2018), and Dicenzo & Levesque (2019). For the only magenta asterisk, the results of Dorda et al. (2018) and Dicenzo & Levesque (2019) are represented after being averaged. The crosses denote the sources measured in this work from the Gaia RVS spectra. The solid black lines mark EW(CaT) = 1.1 nm (for K-type or early M-type RSGs) and the decreasing of EW(CaT) with spectral type (for RSGs later than M2).