What device measures relative humidity?
A hygrometer is used to measure the relative humidity in the air. There hygrometer is also sometimes called the phychometer. The instrument is also used in saunas to measure the amount of water in the air.
A hygrometer. Also, they use a human hair which stretches and shrinks with humidity. Now you know why you get the frizzies on damp days!Google 'human hair hygrometer'
a psychrometer is used to measure humidity. It is composed of a wet bulb thermometer and a dry bulb thermometer