Difference between GSP-Phot metallicities of individual FGK members and the mean [Fe/H] of the parent open cluster for stars with and MARCS models, before and after the calibration. We note that the calibration on LAMOST [Fe/H] values translates [M/H] to [Fe/H]. The red line is the median of the distribution. The blue area is delimited by the 16th and 84th quantiles. Panel (a): residuals versus T_eff before the calibration. Panel (b): residuals versus T_eff after the calibration. Panel (c): residuals versus log g after the calibration.