noun
: a voltmeter employing vacuum tubes and useful because of its very high input impedence for measurements in circuits (as vacuum-tube circuits) from which only very small currents can be drawn without altering the voltages being measured
noun
: a voltmeter employing vacuum tubes and useful because of its very high input impedence for measurements in circuits (as vacuum-tube circuits) from which only very small currents can be drawn without altering the voltages being measured
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012