Influences of selected glass component additions on Abbe's number of a specific base glass, calculated from models for the refractive index and the dispersion. The diagram will change non-linearly for other base glasses. (click image to enlarge)

Abbe's number, ν, is calculated from the refractive index, n, and the dispersion, n_F–n_C, according to various equations. The common ones are:

The subscribts indicate standard wavelengths, λ, at which n is determined, e.g., n_D is measured at 589.3 nm: