Hygrometer

A hydrometer is a device for measuring the humidity in percent. There are different measuring methods. The hair hygrometer bases on the comparison of the length changes of human, animal or artificially produced hair. The psychrometer consists of two thermometers and compares the ambient temperature (measured with one thermometer) with the temperature induced by evaporation (measured with the second thermometer). The most accurate measuring method is the dew point meter, a mirror surface is cooled down until the humidity in the air condenses on it. The relative air humidity is determined by the 3 factors air temperature, mirror surface temperature, and saturation quantities.