Hygrometers are used to measure the relative humidity (water vapor content of the air) in% rel. Humidity.
As a measuring element, human or industrially manufactured (synthetic) hair is used, which expands with increasing humidity. The moisture-dependent change in length is transmitted to the pointer with the aid of a fine mechanism. Due to the special treatment of the hair, FISCHER hygrometers react almost without any inertia to any change in the humidity.