From top to bottom, row 1: standard error factor (see text) as a function of grvs_mag magnitude for the giant star samples. The range of surface gravity of each sample is provided in the legend. The red curve corresponds to the calibration of f_σ provided in Babusiaux et al. (2023). Row 2: same as row 1 for the dwarf star samples. The range of effective temperature of each sample is provided in the legend. Row 3: distributions of the normalised residuals of two groups of stars from the g2 giant sample (see Appendix E), selected in the magnitude ranges grvs_mag ∈ [9.4, 9.9] (left) and [13.8, 14.1] mag (right). Gaussian profiles with standard deviations equal to 1 are overlaid (orange curves).