A magnet suspended in a uniform magnetic field like that of the Earth can be made to oscillate about the field. The frequency of oscillation depends on the strength (magnetic moment) of the magnet, that of the external field, and the moment of inertia of the magnet. It is easily shown and verified by experiment that a simple but nontrivial expression represents this motion well, but that only the product of the magnetic moment and magnetic field can be determined. The repulsion of two magnets can be used to determine the magnetic moment, and in turn the external field can be determined. The results are reasonably good considering the very simple equipment required, and the experiment allows quantitative investigation of magnetism.