Activity index histogram (bin size 0.001 nm, with KDE superimposed) normalised to peak values of stars with T_eff ∈ (4000 K, 5000 K). Left panel: stars with log g >  4.0 (dwarfs) and right panel: stars with log g ∈ (3.0, 3.5). From this latter we estimate an upper limit to the true dispersion of the sample of 0.011 nm and 0.006 nm for the GSP-Spec and GSP-Phot input respectively, and an upper limit to the true bias of ≃0.002 nm (see text for details).