You searched for: “potentiometer
potentiometer (s) (noun), potentiometers (pl)
1. An instrument for measuring an unknown voltage by comparison to a standard voltage: The electrician used a potentiometer to assess the voltage that had been used in the old villa.

A potentiometer is a device that measures electromotive force or potential difference by comparing a part of the voltage to be measured against a known electromotive force.
2. A three-terminal resistor with an adjustable center connection: A potentiometer is widely used for volume control in radio and television receivers.