Left panels: portions of stellar spectra around four Fe i b) and two Ca i a) lines for RGB star 12175. • indicate the observed spectrum. The solid line indicates a synthetic spectrum with  [Fe/H]  = −3.1 and  [Ca/H]  = −2.8. The dotted lines in a) indicate synthetic spectra with  [Ca/H]  ± 0.3 relative to the solid-line-synthetic spectrum. Right panels: Portions of stellar spectra around four Fe i d) and two Ca i c) lines for star 42 241. • indicate the observed spectrum. The solid line indicates a synthetic spectrum with  [Fe/H]  = −2.0 and  [Ca/H]  = −2.6.