Comparisons of the Pristine-Gaia synthetic (top row of the left-hand panels) and Pristine DR1 (bottom row of the left-hand panels) photometric metallicities with the spectroscopic metallicities of the cleaned giant star training set (see text for details). The right-hand panels show the histograms of metallicity differences for the two catalogues, with the Pristine-Gaia synthetic catalogue in blue and Pristine DR1 in red. The catalogues are split as a function of G_BP magnitude, into the bright end (G_BP < 16; top) and the fainter end (G_BP < 16; bottom). At brighter magnitudes than this limit, both catalogues are similarly competitive, as can be appreciated from the confidence interval of the metallicity differences in the right-hand panels (16th to 84th percentiles; vertical dashed lines) and the average of these percentile offsets quoted as σ in the two panels. At fainter magnitudes, the Pristine DR1 catalogue continues to remain very competitive while the Pristine-Gaia synthetic catalogue suffers from the lower signal-to-noise of the CaHK_syn magnitudes, leading to a wider distribution of metallicity differences.