Master Clocks

A master clock is a precision clock that provides timing signals to synchronise slave clocks as part of a clock network. Networks of electric clocks connected by wires to a precision master pendulum clock began to be used in institutions like factories, offices, railway networks, telephone exchanges and schools around 1900.
The clock timing signals, generated by electrical contacts attached to the mechanism, were minute, half minute and sometimes one second electrical pulses, fed to the controlled equipment on pairs of wires. The devices driven could be wall clocks, tower clocks, factory sirens, school bells and occasionally clock chiming mechanisms. “