FPrime is a very useful windows-based utility and visualiser for calculating real and anomalous X-ray dispersion co-efficients. It is very useful for calculation of f’ and f” for different elements at different wavelengths/energies for input into structure refinements carried out against data collected using synchrotron radiation. It was written by Prof. Robert B. Von Dreele (Los Alamos National Laboratory) in 1994 and is available with the GSAS download package. A zip file can be obtained from CCP14.