An engine order telegraph is a communications device used on a ship or submarine for the pilot on the bridge to order engineers in the engine room to power the vessel at a certain desired speed. Traditional E.O.T.s required a pilot wanting to change speed to "ring" the telegraph on the bridge, moving the handle to a different position on the dial. This would ring a bell in the engine room and move their pointer to the position on the dial selected by the bridge. The engineers hear the bell and move their handle to the same position to signal their acknowledgment of the order, and adjust the engine speed accordingly. This image can be used conceptually to indicate movement and direction in, for instance, financial markets.
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