The cost of small digital computers has fallen to a level at which a slow spinner magnetometer using such a machine for data capture and processing is competitive in cost with existing high performance magnetomers. The advantages of using a computer to replace the phase sensitve rectifier and digital read-out of existing machines are many and include: drift free integration over extended time scales, Fourier analysis of the waveform from the sensors, storing of the intermdiate results of the various orientations and combinging these to produce a complete result in terms of total intensity, declination, and dip, while at the same time eliminating any consent magnetic moment of the rotating mechanism. The results are printed and the measuring system allows a very simple method of estimating the errors for any particular integration period. The overall effect is of an instrument which is quick and convenient to use yet which gives results which are at least as good as those from existing machines.