The hygrograph uses the change of length of human hair or synthetic fibres depending on the moisture contained in the air. The special treatment of the hair is the reason for the very low response time, even in case of very low temperatures. For this reason, hair-hygrographs are preferred for outdoor measurements. For measurements in production and in storerooms we recommend the use of hygrographs with synthetic fibres, because they need less maintenance than hair-hygrographs and are less sensitive against contamination.

The movement’s parts consist off brass and are dull chromium plated. All axles are fitted in jewel bearings. Therefore the instruments have got a considerably low idle friction. The sensors are located within the housing and therefore protected against mechanical damage. In spite of this arrangement sufficient ventilation of the sensors is guaranteed. The used materials and the finish are responsible for the high resistance against corrosion.

The hygrographs are alternatively equipped with a mechanical or electronical quartz clockwork. The clockwork can be set to daily, weekly or monthly revolution in next to no time. The time for one revolution will be 25.6 h / 176 h / 783 h (738 h quartz clockwork only). The recording instruments are delivered together with fibre tips and recording charts needed for one year of operation. As an option the devices are available with lockable housing.