Mechanical duct hygrostat HYGRASREG® KH-10 with switching output, as a one-step hygrostat. It works without external voltage and is suitable for controlling and monitoring relative humidity in ventilation and air conditioning ducts, laboratories, production facilities, climatic test cabinets, indoor swimming pools, greenhouses, etc. for controlling humidifying and dehumidifying equipment, as minimum guard, or maximum hygrostat. The KH-10 is applied in dust-free, pollutant-free, non-aggressive air.