Final answer:
Relative Humidity (RH) is measured using a hygrometer or psychrometer. Hygrometers can be electronic or hair-based, which measure moisture levels in the air directly, while psychrometers use the wet-bulb and dry-bulb temperature readings to calculate RH.
Step-by-step explanation:
The two instruments commonly used to measure Relative Humidity (RH) are the hygrometer and the psychrometer. A hygrometer can be electronic and use capacitive or resistive sensors that change their electrical characteristics as humidity changes. It can also be a hair hygrometer where a strand of hair stretches due to absorption of moisture which in turn rotates a dial to show humidity levels.
A psychrometer, on the other hand, is a more traditional tool that uses the concept of wet-bulb and dry-bulb temperatures. It consists of two thermometers, one with a wet cloth (wet-bulb) and one without (dry-bulb). The difference in readings allows calculation of the RH, as the evaporation from the wet-bulb is dependent on the moisture content in the air.