Shortt's breakthrough in 1920 came with the development of a clock system, inspired by the work of R.J. Rudd of Croydon, championed by Hope-Jones, in which the task (each thirty seconds) of unlocking the impulse to an otherwise free pendulum was taken on by a separate slave clock, which in turn was corrected (as part of the same operating cycle) by a synchronising pulse derived from the master clock, containing the free pendulum.