barograph

An aneroid-type barometer fitted with a device capable of continuously recording atmospheric pressure. The oscillations undergone by the aneroid capsule - as a result of pressure changes - are transmitted to a pen that rests on graduated paper mounted on a rotating drum. The inked needle traces a graph on the paper, faithfully reproducing the pressure variations, with their continuous rises and falls. The instrument must be calibrated frequently (ideally every 24 hours) against a mercury barometer, given the greater precision of the latter instrument.