[Fe/H] calibration based on members of open and globular clusters. Top left panel: One-to-one comparison of the xgb_met values for open and globular cluster members with spectroscopic [Fe/H] measurements from the literature (using Joshi et al. 2024 for open clusters and Harris 2010 for globular clusters). Second row: residuals between xgb_met and literature [Fe/H] (left panel) and feh_calibrated and literature [Fe/H], showing the improvement achieved by our proposed calibration. Top right panel: comparison of the three metallicity distributions (literature, xgb_met, and feh_calibrated) for the cluster sample.