Δ [Fe/H]  (in the sense ours minus GCSII) as function of T_eff (panel a)) and  [Fe/H]  (panel b)) for stars in the irfm sample satisfying the applicability range of our metallicity calibration. Notice the two breaks at 5500 K and 6500 K which correspond to the discontinuities introduced by the three calibrations used in GCSII for different (b − y). Contour levels and lines as in Fig. 2.