Comparison of different CaT-[Fe/H] calibrations to independent Fe-abundances from iron-line analysis for the same sample of stars. In each panel Δ [Fe/H] = Fe − CaT. We show the results for our complete sample in open circles and highlight stars with S/N ≥ 25 and σ [Fe/H] ≤ 0.15 with filled symbols. The red and green dashed line in each panel indicate the best linear fit to the Starkenburg- and Carrera-calibration, respectively, and reveal a constant ~ 0.2 dex-offset between them. The latter one yields a better fit to our data. The classical GC-calibration in the top panel shows a clear systematic trend for [Fe/H] ≤ − 1.8, resulting in CaT-metallicities too metal-rich by as much as 0.5 dex.