The core program of the main fitting routines as used at Liverpool is called ``fcfcore'' which contains code to read and write the data files, vary the parameters and perform minimisation (using NAG routine E04FCF). The physics which determines the line positions and intensities is contained in separate subroutines, making it easy to alter and add new types of fitting routines.
For most spectra a general purpose subroutine called ``FFitA'' is used. This can produce multiple singlets, doublets or sextets using Lorentzian lineshapes. To reduce the computing time necessary for fitting it uses the approximations described in Section 2.3.4.
For spectra with distributions of hyperfine field or quadrupole splitting values a program called NORMOS/DIST is used. This is an extension to the NORMOS/SITE fitting package. This uses the VA02A routine for minimisation. The routines can fit with multiple hyperfine field or quadrupole splitting distribution blocks as well as multiple crystalline sites.