What does a tachometer measure?

A tachometer is an instrument specifically designed to measure the rotational speed of a shaft or disc, typically expressed in revolutions per minute (RPM). This makes it essential in applications where speed control is critical, such as in automotive engines, industrial machinery, and various electronic devices. By providing real-time feedback on the speed of rotation, tachometers help ensure optimal performance and efficiency.

In contrast, devices that measure voltage levels, current flow, or temperature fluctuations are fundamentally different instruments with distinct purposes and functions. Therefore, the focus of a tachometer on measuring the speed of rotation sets it apart and confirms the choice as the correct answer.