Barometer
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Barometer is a instrument used to measure air pressure. The barometer measures air pressure in units called hectopascals (hPa). Air pressure and differences in pressure are among the most important ways to describe or measure weather. Therefore the barometer is important for meteorologists.
There are various types of barometers such as the water barometer, aneroid barometer, and the mercury barometer. They were invented by an Italian mathematician named Evangelista Torricelli in 1643.