Barographs use one or more aneroid cells acting through a gear or lever train to drive a recording arm that has at its extreme end either a scribe or a pen. A scribe records on smoked foil while a pen records on paper. The recording material is mounted on a cylindrical drum which is rotated slowly by clockwork. Commonly, the drum makes one revolution per day, per week, or per month and the rotation rate can often be selected by the user.
As atmospheric pressure responds in a predictable manner to changes in altitude, barographs may be used to record elevation changes during an aircraft flight. Barographs are required by the FAI to record certain tasks and record attempts associated with sailplanes. A continuously varying trace indicates that the sailplane has not landed during a task, while measurements from a calibrated trace may be used to establish the completion of altitude tasks or the setting of records. Examples of FAI approved sailplane barographs include the Replogle mechanical drum barograph and the EW electronic barograph (which may be used in conjunction with GPS).
Nowadays, mechanical recording barographs have commonly been superseded by electronic weather instruments that use computer methods to record the barometric pressure. These are not only less expensive than mechanical barographs but they may also offer both greater recording length and the ability to perform further data analysis on the captured data including automated use of the data to forecast the weather.