Illustration of the CaT co‐addition in a high‐S/N spectrum of a red giant in a calibration globular cluster (star N3201‐S11; ﹩\mathrm{S}\,/ \mathrm{N}\,\sim 110﹩, ﹩V=14.5﹩ mag, ﹩v_{\mathrm{HC}\,}=485﹩ km s⁻¹, and ﹩\langle \Sigma W\rangle =3.8﹩ Å) and a low‐S/N DEIMOS spectrum of a M31 red giant (star 5004266; ﹩\mathrm{S}\,/ \mathrm{N}\,\sim 4﹩, ﹩V=21.7﹩ mag, ﹩v_{\mathrm{HC}\,}=-338﹩ km s⁻¹, and ﹩\langle \Sigma W\rangle =2.4﹩ Å). Left: Each individual Ca line, shifted to a common line center. Right: Weighted co‐added line (solid line), from which we measure the CaT line strengths using a Penny (i.e., Gaussian plus Lorentz profile) fit (dashed line).