The maintenance of a truly constant speed under conditions of varying load is beyond the capability of a centrifugal governor, an increase in load being associated with a fall in speed coterminous with the increase. If, however, the speed is controlled by comparison with some reliable standard of frequency it may be made synchronous with this standard except during those periods when the load is actually changing.In the apparatus described here the speed of an electric motor is synchronized with a pendulum clock and it is shown that the arrangement will apply corrections for speed deviations as small as ±0.03% on nominally constant loads, and will correct variations as large as ±7.5% which may be caused by changing loads.