Relation between GC S/N and absolute g-band magnitude from the ACSFCS catalogue (top), LOS velocity uncertainty (middle) and metallicity uncertainty (bottom) for the sample of F3D GCs. The vertical line marks S/N = 8 Å⁻¹, our limit for the metallicity measurement. In the top panel, we only show GCs with M_g from the ACSFCS while the middle and bottom panel also include GCs that were not included in the catalogue of Jordán et al. (2015).