Example of the small (compared to the errors and internal spreads) residual offsets in [Fe/H] between UVES and GIRAFFE in GES iDR4 data, in two of the sample GCs: NGC 2808 (top panels) and NGC 1851 (bottom panels). The left panels show [Fe/H] as a function of T_eff and the right panels show [Fe/H] as a function of log  g. The UVES stars are plotted as cyan symbols with their median [Fe/H] as a cyan line. The GIRAFFE stars are plotted as magenta symbols with their median [Fe/H] as a magenta line. The reference [Fe/H] from Harris (1996, 2010) is plotted as an orange line.