Abstract: Gear pitch testing apparatus has a computer control for programming relative displacements between a gear and a pair of probes, and means for automatically comparing test data with stored reference values to indicate deviations in the gear under test. Initial setting of the apparatus for a test sequence requires the operator only to control the relative displacements of the gear and probes to synchronise them approximately, the coarse adjustment thus obtained then being automatically modified in an electronically controlled fine adjustment stage to co-ordinate the movement between the gear and the probes accurately and allow such characteristics as absolute cumulative pitch error to be evaluated.