barograph

A barograph (from the Greek βάρος báros "heaviness, weight" and γράφειν gráphein "to write") is a measuring device that records the temporal variation of air pressure on a drum covered with paper. The resulting curve is called a barogram. A barogram of this type can be seen at the top right. The analysis of the barogram can give the expert clues about future weather developments. Barographs are particularly common on ships. A sharp drop in pressure within a period of one to three hours can be an indication of approaching strong winds or a storm. A barometer is used for the actual measurement.