Metallicity as a function of galactocentric distance, R, for the bulge of M31. Positive and negative values of R correspond to opposite sides of the slit. The top and bottom panels show [Fe/H] and [M/H], respectively. Lines with different colors refer to E-MILES BaSTI (blue) and Padova00 (red), and Cvd18 models (green), respectively. Thick and thin lines indicate 1SSP and 2SSP models, respectively, while solid, dashed, and dotted lines plot results of different methods, i.e., full-spectral fitting, full-index fitting, and index fitting, respectively, as shown by the labels in the top panel. Median trends are plotted as black curves with black dots.