Top panels: metallicity of individual OCs of the sample derived from three Gaia XP-based catalogues (on the Y axis) presented against that from three high-resolution spectroscopic surveys (on the X axes of the left, middle and right plots). Bottom: difference between the two values for each cluster. The same colour-coding scheme applies as in Fig. 1. The 1:1 relation is shown by the diagonal black line in the top plot and, respectively, by the horizontal line indicating zero difference in the bottom plot. The number in the top corner indicates the median difference and the root mean square difference (RMSD) of the respective catalogue.