An instrument that measures atmospheric pressure is called a barometer. Barometers are critical tools in meteorology, helping forecast weather conditions by detecting changes in air pressure. There are different types of barometers, including mercury barometers and aneroid barometers. Mercury barometers use liquid mercury in a glass tube to show pressure levels, while aneroid barometers utilize a sealed metal chamber that expands or contracts in response to pressure changes. Understanding atmospheric pressure is vital for predicting weather patterns and phenomena such as storms, making barometers essential for both professionals and hobbyists in the field of meteorology.