What tool is used to measure atmospheric pressure?

The correct answer, which is a barometer, is specifically designed to measure atmospheric pressure. It operates by detecting changes in pressure exerted by the atmosphere on the instrument itself. The barometer is vital in meteorology, as it helps in forecasting weather by indicating high or low-pressure systems.

A manometer is primarily used for measuring the pressure of gases or liquids in closed systems, not atmospheric pressure. A thermometer measures temperature and does not provide any information regarding atmospheric pressure. A hydrometer is used to measure the specific gravity of liquids, which is unrelated to pressure measurement. Understanding these distinctions clarifies why the barometer is the appropriate tool for measuring atmospheric pressure.