Master clock

Modern radio clocks are synchronised by radio signals or Internet connections to a worldwide time system called Coordinated Universal Time (UTC), which is governed by primary reference atomic clocks in many countries.

It generated periodic timing signals by electrical contacts attached to the mechanism, transmitted to the controlled equipment through pairs of wires.

The controlled devices could be wall clocks, tower clocks, factory sirens, school bells, time card punches, and paper tape programmers that ran factory machines.

An example is the GPO time service in Britain which distributed signals from the Greenwich Observatory.

The UK had four such manufacturers, all of whom made clocks to the same GPO specification and which used the Hipp Toggle impulse system; these were Gent and Co., of Leicester, Magneta Ltd of Leatherhead in Surrey, Synchronome Ltd of Alperton, north-west London, and Gillett and Johnson.

Master clock (at left) driving several slave clocks in an enthusiast's garage. The third one from the left at the top is a radio-controlled clock for reference.
The master atomic clock ensemble at the U.S. Naval Observatory in Washington, D.C. , which provides the time standard for the U.S. Department of Defense. [ 1 ] The rack-mounted units in the background are HP 5071A caesium beam clocks. The black units in the foreground are Sigma-Tau MHM-2010 hydrogen maser standards.