Abbe number and glass code

Abbe number:

V =

nD - 1 nF-nC

(1)

where n_D, n_F and n_C are the refractive indices of the material at the wavelengths of the Fraunhofer D-, F- and C- spectral lines (589.2 nm, 486.1 nm and 656.3 nm respectively). Low dispersion (low chromatic aberration) materials have high values of V [1].

Glass code:
Example of BK7:
517642
n = 1.517
V = 64.2
(both at 587.56 nm) [2]

References:
[1] http://en.wikipedia.org/wiki/Abbe_number
[2] http://en.wikipedia.org/wiki/Glass_code