Spectral indices as a function of the adopted spectral types for our new ultracool subdwarfs. Typical uncertainties on the spectral indices are of the order of 0.1 (cross at the bottom of each plot). Uncertainties on the spectral types are 0.5 subclass. Top left: adopted spectral types vs. TiO5 index. Top right: adopted spectral types vs. CaH1 index. Bottom left: adopted spectral types vs. CaH2 index. Bottom right: adopted spectral types vs. CaH3 index.