The device used to measure atmospheric pressure is called a barometer. Barometers are essential tools in meteorology, allowing scientists to forecast weather changes by measuring the weight of the air above the instrument. As atmospheric pressure fluctuates, it can indicate whether conditions are likely to be clear, windy, or stormy. There are two main types of barometers: mercury barometers, which use liquid mercury to measure pressure, and aneroid barometers, which rely on a flexible metal chamber that expands and contracts with changes in pressure. Both types are crucial for understanding weather patterns and predicting changes in our environment.