Again, in this figure, we use the 3.6 Å resolution flux spectra. The negative luminosity effect in the Ca I 4227 line is the most striking luminosity indicator in the M2 stars. At this resolution, the morphology of the MgH/TiO blend near 4770 can be used as well to distinguish luminosity classes; notice that the MgH band dominates this blend in the dwarf star, producing a tooth-shaped feature. The morphology of the spectral region between 4900 and 5200 Å seems as well to be sensitive to luminosity. At higher resolutions, other features, especially in the blue-violet region, can be used.