Comparison of the [Fe/H], [Ca/H], and [Mg/H] estimates from SDSS/SEGUE and BOSS stars obtained by fitting individual lines with the metallicity results determined in Paper I, [M/H], which considered the entire spectrum in the analysis. The mean difference between x and y axes appears in the top left corner of each panel, evaluated in three ranges of [M/H]: [M/H] > −1.5, −2 < [M/H] < −1.5, and [M/H] < −2, and the corresponding standard deviations are written in the bottom right corner. The top panels show good agreement between [Fe/H] inferred from individual lines of this element, with an offset of ~0.1 dex. [Ca/H] estimates are offset by ~0.4 dex over [M/H], except at metallicities higher than [M/H] = −1.5, as expected. [Mg/H] estimates display a higher dispersion, increasing with decreasing metallicity, and lower deviations for BOSS stars with respect to SDSS/SEGUE stars.