A barometer is a scientific instrument that is used to measure air pressure in a certain environment. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis to help find surface troughs, pressure systems and frontal boundaries.

Barometers and pressure altimeters (the most basic and common type of altimeter) are essentially the same instrument, but used for different purposes. An altimeter is intended to be used at different levels matching the corresponding atmospheric pressure to the altitude, while a barometer is kept at the same level and measures subtle pressure changes caused by weather and elements of weather. The average atmospheric pressure on the earth's surface varies between 940 and 1040 hPa (mbar). The average atmospheric pressure at sea level is 1013 hPa (mbar).

Barometer consisting of a rheostat and a capacitor, a barometer measures the atmospheric pressure by calculating changes in electrical resistance and capacitance.

Barometer corrects altitude measurement errors to narrow down the deviation to about 1 meter and works with your phone's GPS to locate the position when you are under an overpass or inside a high-rise building.

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