Differences between the spectroscopic and photometric metallicities as a function of spectroscopic metallicity for APOGEE VS, for [Fe/H]_phot, v (upper panel) and [Fe/H]_phot, b (lower panel). The horizontal grey lines are located at Δ[Fe/H] = ±0.5 dex. The continuous red lines trace P₅₀ and the dashed red lines P₁₆ and P₈₄ of the Δ[Fe/H] distribution. A shift of +0.14 dex has been applied to [Fe/H]_phot, v to minimise the median Δ[Fe/H] in the region [Fe/H]_spec ≤ −0.8, while a shift of −0.36 dex was applied to [Fe/H]_phot, b to minimise the median Δ[Fe/H] in the region [Fe/H]_spec ≥ −0.8.