noun
voltmeter
A device for measuring voltage. Technical term used in electronics and electrical engineering.
電圧計でバッテリーの電圧を測った。
I measured the battery voltage with a voltmeter.
テスター is a more general term for a multimeter that can measure voltage, current, and resistance, while 電圧計 specifically refers to a voltmeter.
Compound of 電圧 (voltage) + 計 (meter, gauge).