Differences between the exact spectra (computed by adopting consistent [α/Fe] ratios in the model atmosphere and the spectral synthesis) and the corresponding AMBRE ones. The computed differences correspond to the exact spectrum minus the corresponding AMBRE spectrum. The [α/Fe] ratio of the adopted model atmosphere for the AMBRE spectra of the left panel is always +0.2 dex, while the spectral synthesis was performed assuming [α/Fe] = +0.0. In the right panel, the adopted model atmosphere for the AMBRE spectra are for [α/Fe] = +0.2, while we assumed [α/Fe] = +0.4 for the spectral synthesis. The effective temperature and surface gravity of the exact and AMBRE spectra is indicated in the different panels. All spectra (exact and AMBRE ones) have [M/H]  =  −0.5 and [α/Fe] = +0.0 or +0.4 as indicated in the figure title (left and right panels, respectively).