[Fe/H]_e vs. T_eff diagrams published in H16 (top panel, with [α/Fe] = 0) and those obtained with FERRE using GSL and the three different interpolation schemes (other panels, with [α/Fe] = +0.4). The measurements of individual spectra are shown as blue dots, and the nodes of the grids are overlaid as thin crosses. The red dots and line are the mean [Fe/H]_e in bins of 250 K, and the error bars are the dispersion in these bins.