Observed (black circles) and synthetic spectra for a star (OGLE26-415574) in the field HRm5m3 zoomed into the region used to derive Ca (upper panel) and Mg (lower panel) abundances. The synthetic spectra created with the best-fitting Ca ([Ca/Fe] = 0.06) and Mg ([Mg/Fe] = 0.05) abundances are shown in solid red lines. The elements producing the strongest absorption lines are marked in each panel. For each spectral region we show a zoomed-in section around the Ca line at 6166.4 Å and the Mg triplet that includes the synthesis produced using the best-fitting abundance as red solid lines. In blue and green we show the synthetic spectra using a 0.1 dex abundance variation around the best-fitting value. The Y-axis of both zoomed-in regions have the same scale with normalised fluxes that range from 0.8–0.5 for Ca and 1.0–0.7 for Mg lines.