Maker's Name: 
International Time Recording Co. Ltd / IBM
Where made: 
circa 1940(?)
19 × 31 × 131 cm

This item is a Pendulum Master clock, made by International Business Machines in the United Kingdom around 1963. The wooden case holds the clockwork and pendulum and above the case is a connected dial. Dials such as these are called slave dials and could be placed throughout an entire building, with all the dials being driven by the same Master Clock, thus ensuring each room was given the same time.

The slave dial is controlled by a set of wires that connect it to the master clock. Every 60 seconds a circuit in the master clock is closed and this sends an electric pulse through the wire and into the slave dial. This moves the minute hand one tick. The circuit closer is called an impulse control. Because the information is carried from the master clock to the slave dial via electricity, the slave dial can be placed in a different room or even on a different floor, the only requirement is that the wires are able to reach the master clock.

The master clock has a spring inside of it that drives the pendulum. The clockwork represents the result of 300 years of development since Christian Huyghens operated the first pendulum clock on Christmas day 1656. The pendulum rod is made of the low expansive alloy ‘invar’ which was discovered by Charles Guillaume. Guillaume was awarded the Nobel prize in 1920 for this. The escapement is of the deadbeat type, introduced by George Graham in 1715. The mechanism is driven by a small spring, rewound every minute for two seconds to maintain a constant torque. If the clock was to lose power it could run off the wound spring for up to eight hours. If there is no electricity the slave dial will not move. The master clock has a wheel that is turned one way by the spring and the opposite way by the electricity. When the electricity is flowing the two forces are stationary and the wheel does not turn. When the electricity is cut off the wheel will turn under the force of the spring. When the power is turned back on the clock will use the wheel to calculate how much time has elapsed and will send the appropriate amount of pulses to correct the slave dials time.

When the slave clocks hand reaches one minute to the hour, a mechanism cuts off the usual electric pulse from the master clock. It then receives a series of pulses from another wire from the master clock which will cause a lagging minute hand to catch up. This is done to ensure that the clock is not lagging or too far ahead.

International Business Machines, or IBM, was created on June 16, 1911 when three 19th century companies decided to merge and become the Computing Tabulating Recording Company, based in the United States. These companies were The Tabulating Machine Company, The International Time Recording Company and The Computing Scale Company of America. In 1924, the Computing Tabulating Recording Company changed its name to International Business Machines Corporation.

Today IBM is a multinational technology and consulting corporation.

.This item is part of the UQ Physics Museum Electric Clocks Tour

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