Operating an engine order telegraph required a pilot to move the telegraph handle to a different position on the dial (sometimes called telegraph face). This would ring the bell in the engine room and move the 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.
Hammerhead engine order telegraphs, steering stations and binnacles on the bridge aboard ocean liner Queen Mary.
Researched & Compiled by Susan Donnelly