(a) Same as Figure 1 for SZ Cen, with [Fe/H] = −0.25. (b) ﹩{\alpha }_{\mathrm{MLT}}﹩ for both stars restricted to the CB2018 value of ﹩{{\alpha }_{\mathrm{MLT}}}_{\odot }=1.60﹩ (dots), or to a value of 1.80 near our solar-calibrated mixing length (squares). (c) Same as panel (a), adding the constraint from the measured temperature ratio (see text). (d) Same as panel (b), adding the constraint from the measured temperature ratio. (e)–(h) Same as panels (a)–(d), for [Fe/H] = −0.20.