Difference between the GES recommended APs and [Fe/H] and the photometric reference APs and literature [Fe/H] (see text for more details). The GES iDR4 results are plotted as blue triangles (for GIRAFFE) and red circles (for UVES). Grayed-out symbols represent the previous internal release (iDR2 + iDR3) corresponding values. The top panel shows ΔT_eff as a function of GES [Fe/H], the middle panel Δlog g as a function of GES [Fe/H], and the bottom panel Δ[Fe/H] as a function of the literature reference [Fe/H]. The median internal errors of GES recommended values are also plotted at the center of each panel.