Ratios of [K/Mg] versus [Sc/Mg] from those models selected from Fig. 4 that have either a C-O shell merger or initial metallicity Z_ini<10⁻⁵. The adopted solar reference is from Asplund et al. (2009). The different colored labels identify each set of models as in Fig. 4 (see side legend). Different symbols identify different initial masses (see top legend). Models with and without a C-O shell merger are represented by a filled and empty symbol, respectively. The blue star symbols are observations of low-mass stars of low metallicity taken from JINAbase (Abohalima & Frebel 2018) with [Fe/H] < −3. A representative error bar for the observation data is shown, as taken from Roederer et al. (2014). The dashed vertical and horizontal lines represent the average [K/Mg] and [Sc/Mg] ratios from the observations. The gray shaded area represents the representative error bar for the average data point.