What does the term "engine order telegraph" refer to?

The term "engine order telegraph" refers to a communication device that is used to convey engine speed orders from the bridge to the engine room. This device allows the bridge crew to send commands to the engineering team regarding the desired speed and direction of the vessel, facilitating coordination between the two departments.

The engine order telegraph operates by transmitting signals that can be seen and heard by the engineers in the engine room, ensuring that they can respond appropriately to the captain's orders. This system is crucial for safe and effective vessel operation, especially during maneuvers that require precise adjustments in engine power.

The other choices represent different aspects of ship operations but do not encompass the primary function of the engine order telegraph. Measurements of engine temperatures, monitoring fuel levels, and alerting the crew of engine failures are all distinct and critical functions handled by separate equipment and systems on a vessel.