barograph

A barograph (Ancient Greek βάρος báros "heaviness, weight" and γράφειν gráphein "to write") is a measuring device that records the variation of air pressure over time on a drum covered with paper. The resulting curve is called a barogram. On the right-hand side above you can see such a barogram. The evaluation of the barogram can give the expert indications for the future weather development. Barographs are often found on ships. A strong drop in pressure within a period of one to three hours can be an indication of approaching strong winds or storms. A barometer is used for the actual measurement.