The calibration devices are small, hermetically sealed chambers, adapted exactly to each type of ROTRONIC sensor. The lower part consists of a screw-on lid, inside which the humidity standard and a textile pad are placed. After an acclimatization time, the ambient humidity in the calibration device corresponds exactly to the specified humidity value. The longer the acclimatization time, the higher the humidity. The sensor can then be calibrated or adjusted against the standard.