The instrument, designed primarily for the determination of average nuclear counting rates, incorporates the following circuit features: (1) biased diode for establishing the recording level; (2) frequency meter using a triggered blocking oscillator, the average plate current of which is proportional to the rate of arrival of pulses; (3) provisions for the operation of a mechanical impulse counter at low rates. A resolving time in the vicinity of 1 microsecond can be achieved.