Top panel: spectral subtype of the templates as a function of the CaH2 spectral index. Points are colored by the template MC. The CaH2 to spectral type calibration from J. E. Gizis (1997) is shown in black. The subtypes of our templates are consistent with the historical definition of low-mass spectral subtypes for K5.0–M6.0. There is some deviation for later subtypes, though this is expected for ultra-cool dwarfs when the VO molecular band begins to dominate. Middle panel: ζ_TiO/CaH spectral index of the templates as a function of MC, colored by ST. As the metallicity of a star decreases, so too should the ζ_TiO/CaH. The negative correlation between ζ_TiO/CaH with MC demonstrates that MC is also correlated to metallicity. Bottom panel: CaH2+CaH3 spectral index as a function of the TiO5 index. Lines of iso-zeta_TiO/CaH that define the four traditional metallicity classes from S. Lépine et al. (2007) are overplotted in black. We use these lines to determine which template MCs represent dwarfs (red), subdwarfs (yellow), extreme subdwarfs (green), and ultra-subdwarfs (blue).