What device is used to measure relative humidity?

The device used to measure relative humidity is a hygrometer. A hygrometer specifically measures the amount of moisture in the air, which is essential for understanding environmental conditions in various contexts such as HVAC systems, meteorology, and indoor climate control.

Hygrometers typically use different methods to measure humidity, including electronic sensors, hair strands that expand and contract with moisture levels, or hygroscopic materials that absorb water. The primary function is to provide readings that indicate the relative humidity percentage, which is crucial for applications that require precise moisture control.

In contrast, a thermometer measures temperature, a barometer measures atmospheric pressure, and a manometer measures the pressure of gases or liquids in a closed system. Each of these devices serves distinct purposes and does not provide information about humidity levels.