FOURDEM: a program written as an aid to teaching the elements of Fourier synthesis and other crystallographic concepts

A program is described which demonstrates in two dimensions the principles of Fourier synthesis. There are two versions of the program, written in Absoft Fortran for use on a Macintosh II computer: a manual version in which the student can type in values of h, k, |F| and phase angle φ, and an automatic version in which a file of prepared input data can be used. The program can be used to demonstrate the meaning of Miller indices; the relationship between the (hkl) planes and the diffraction pattern; the meaning of phase; Fourier summation; Patterson functions; difference Fourier synthesis; heavy-atom methods of phase determination etc.