A tachometer is primarily used for measuring what?

A tachometer is an instrument specifically designed to measure the rotational speed of an object, typically expressed in revolutions per minute (RPM). This makes it a crucial tool in various applications, especially in automotive and industrial settings, where monitoring the speed of engines, turbines, or other rotating machinery is essential for performance and safety.

Understanding the application of a tachometer allows for better monitoring of equipment performance and can help prevent mechanical failures due to over-revving or improper operating speeds. In contrast, the other options pertain to electrical measurements rather than rotational speed; voltage, current, and resistance are all fundamental electrical parameters measured by different types of instruments. Therefore, the primary purpose of a tachometer is clearly focused on measuring RPM.