Log(Ar²⁺ /O²⁺) (top) and log((Ar²⁺+Ar³⁺)/O²⁺) (bottom) as a function of the ionisation degree, O²⁺/O, for DESIRED-E sample of H II regions (blue circles) and SFGs (black squares). The black dashed lines and the grey bands show the solar log(Ar/O) value and their associated uncertainty, respectively, from Asplund et al. (2021). The different curves represent the ICF(Ar) schemes used in this study: Amayo et al. (2021, shown as red dashed-dotted lines), Izotov et al. (2006, shown as dotted lines with colours corresponding to three metallicity ranges,) and Pérez-Montero et al. (2007, shown as green dashed lines).