Predicted present-day azimuthal variations in the [Ca/H] (first column), [Fe/H] (second column), and [Ca/Fe] (last column) ratios, computed at different galactocentric distances with the 2D chemical evolution model by Spitoni et al. (2023) with multiple spiral structures. We assumed that for the last 1 Gyr (first row, models A+C3 in Spitoni et al. 2023), 3 Gyr (second row), and 5 Gyr (third row), the co-rotation is extended at all distances. The solid coloured lines indicate the variations at co-rotation loci for the three spiral structures that are characterised by the different pattern speeds indicated in Fig. 1 of Spitoni et al. (2023) before they are extended to all radii.