Final answer:
A mercury barometer measures atmospheric pressure in inches Hg and can be used as an altimeter.
Step-by-step explanation:
A barometer is a device that measures atmospheric pressure. A mercury barometer, such as the one shown in Figure 11.16, is one type of barometer. It measures atmospheric pressure in inches Hg. The height of the mercury in the tube is a representation of the atmospheric pressure. When atmospheric pressure varies, the mercury in the barometer rises or falls, providing information for weather forecasting and also allowing it to be used as an altimeter.