What is the function of a tachometer?

A tachometer is a crucial instrument in small engine technology, primarily designed to measure the rotational speed of an engine, typically expressed in revolutions per minute (RPM). This measurement is vital for several reasons: it helps operators understand engine performance, avoid overspeeding, and ensure optimal performance during operation. Monitoring RPM can also assist in diagnosing issues within the engine, as abnormal readings may indicate problems such as misfiring or mechanical failure.

The other options may relate to various aspects of engine operation, but they do not describe the primary function of a tachometer. Torque measurement is important for understanding engine power but is not the focus of a tachometer. Engine temperature assessment is critical for maintaining engine health but typically involves a different instrument, like a temperature gauge. Voltage output from spark plugs is relevant for ignition performance, but this too is outside the scope of what a tachometer measures. Therefore, the role of the tachometer clearly aligns with determining engine speed, making it the correct choice.