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A barometer is a tool meteorologists use to measure atmospheric pressure, which is defined using millibars (mb). The layers of air in the Earth’s atmosphere has weight to it - which is pulled toward the planet’s surface by gravity. During “high pressure” there is more air mass exerting pressure on the surface below, resulting in a "heavier" weight compared to a low pressure system. The barometer measures and tracks these changes in the Earth’s atmosphere, therefore helping meteorologists forecast weather conditions in the short-term.

The first mercury barometer was created in the 1600s by an Italian physicist and mathematician Evangelista Torricelli. was inspired by Galileo Galilei, who built a thermometer that measured temperature using a glass tube and water. Torricelli began using his own vacuum theory to gauge air pressure and make predictions from there.

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Barometers have come a long way since the 1600s. In the early years of the barometer, people used them as status symbols, hanging them in their homes to show wealth. Now, pretty much everyone who owns a smartphone has a barometer - because they are built-in the tiny devices we carry around in our pockets. They are used to help determine elevation, which helps with our GPS tracking by determining exactly where we are at any given time.

J​ennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.