Examples of LTE (black) and NLTE (red) curves of growth for spectral lines of three different elements in Arcturus. Solid lines represent the results of this work and dashed lines correspond to the results of Lind et al. (2011) for Na, Osorio & Barklem (2016) for Mg, and Nordlander & Lind (2017) for Al. The black dotted line in the middle panel has been computed with model atmospheres that have consistent [α/Fe] ratios as explained in the text.