Systematic uncertainty for the stellar velocity dispersion as a function of the (a) EW and (b) S/N of Ca IIλ8542. The dashed line represents the equality between the observed σ_* and the value obtained after degrading the spectra quality; dot-dashed and dotted lines represent the 0.1 and 0.2 dex scatter, respectively. At the bottom of each panel, the normalized histograms show the distribution of EW or S/N values obtained for the PG quasars, CARS AGNs, and the inactive galaxy subsample taken from the AMUSING++ survey.