The spectra of hot stars, earlier than A4, can be used to remove atmospheric features. The features differ slightly from those identified at higher resolution, but still prove useful in classifying a star.
Several features demonstrate a dependence on the effective temperature and gravity.
Fifteen stars with particularly high and low metal abundances are included in the catalog and a dependence on metal abundance is also found. The ratio of the equivalent widths of the absorption features Mg I to 1.16um correlates with the luminosity class of a star, with a higher ratio for lower luminosity classes. Using these two indicators a star can be classified to within several subclasses.