A simple method of maintaining the position of the mercury meniscus of a manometer within less than 1 mm when pressure changes across the meniscus occur at a rate of up to 1 cm of mercury per minute. The limits of movement of the meniscus are determined by electrical contacts inserted through the manometer wall. The balancing of a pressure change across the meniscus is effected by the movement of a mercury reservoir raised or lowered by the rotation of a bobbin controlled by an electromagnetic ratchet relay. Each movement of the reservoir is recorded by an electromagnetic hammer.