baromeeter

A barometer is an instrument that measures atmospheric pressure, the weight of the air above a location. Barometric readings are used in weather forecasting and climate study, and they can help estimate altitude when combined with temperature. Modern barometers come in several forms, including mercury, aneroid, and digital devices.

Mercury barometers use a glass tube inverted into a pool of mercury, and the column height balances the external air pressure. Aneroid barometers contain a sealed flexible metal chamber whose deflection drives a pointer. Digital barometers rely on electronic sensors and display readings electronically.

Common pressure units are hectopascals (hPa) or millibars (mb), with 1 atm defined as 1013.25 hPa. At sea level, average pressure is about 1013 hPa, but readings vary with weather and altitude.

The barometer was invented in 1643 by Evangelista Torricelli, who used mercury to demonstrate that air has weight. The aneroid barometer, a liquid-free alternative, was developed in the 1840s by Lucien Vidie.

Applications span meteorology, aviation, and consumer devices such as altimeters in hiking. Limitations include temperature sensitivity, calibration drift, local elevation effects, and the need for periodic recalibration to maintain accuracy.