Выражение встречается в следующем контексте:
The stability control potentiometer will have been pre-set and should normally not require adjustment, but should this be required, usually identified by oscillation of the voltmeter, refer to Fig.6a, 6b for control potentiometer location and proceed as folows:
Колебания показаний вольтметра/колебание напряжения?

Заранее спасибо