2.2 Dispersion
We have indicated nF-nC and nF'-nC' as the main dispersion.
Abbe numbers were determined from the following 
- and
formula and calculated to the second decimal place:
We have also listed 12 partial dispersions (nx-ny), 8 relative partial dispersions for the main dispersion nF-nC and 4 for nF'-nC'.
To make achromatization effective for more than two wavelengths, glasses which have favourable relationships
between and the relative partial dispersion
x,y for the wavelengths x and y are required. These
may be defined as follows:
