Which instrument is used to measure atmospheric pressure?

The instrument used to measure atmospheric pressure is a barometer. Barometers operate on the principle that changes in atmospheric pressure can be detected and quantified. A common type of barometer is the mercury barometer, which consists of a glass tube filled with mercury that rises and falls in response to atmospheric pressure changes. When the atmospheric pressure increases, it pushes down on the mercury, causing it to rise in the tube. Conversely, when the pressure decreases, the mercury level drops. This measurement can be used for various applications, including weather forecasting, since changes in atmospheric pressure often indicate changes in weather conditions.

Other instruments listed have different specific uses: a thermometer measures temperature, a hydrometer assesses the density of liquids, and a pedometer tracks steps taken by an individual as a measure of distance traveled while walking or running.