Abundance ratios of [Ca/Mg] as a function of [Ca/H] in several GCs. In all three panels the empty squares indicate stars with UVES spectra in our FLAMES survey from Carretta et al. (2010b, 2009b, 2010c, 2011, 2013b, 2014, 2015). In each panel a few GCs are highlighted. Left panel: NGC 4833 (Carretta et al. 2014, red squares), NGC 6809 (Carretta et al. 2010b, 2009b: blue squares), NGC 2808 (Carretta 2015: black squares), and NGC 5139 (ω Cen, Norris and Da Costa 1995: orange triangles). Middle panel: NGC 2419 (Cohen & Kirby 2012; Mucciarelli et al. 2012: blue circles) and ω Cen from APOGEE infrared data (Mészáros et al. 2020, green triangles). Right panel: NGC 7078 (M 15: Carretta et al. 2010b, 2009b: red squares), NGC 1904 (Carretta et al. 2010b, 2009b: black squares), NGC 6093 (M 80: Carretta et al. 2015: magenta squares), and NGC 6715 (M 54: Carretta et al. 2010c: cyan squares). The different vertical scale in all panels should be noted.