The versatile instrument for measuring air humidity, U-value, material equilibrium moisture and pressure dewpoint in compressed air systems. The humidity sensor, developed by Testo, has proven itself worldwide and has excellent features in terms of precision, long-term stability, temperature resistance and robustness. Up to 3 temperature or humidity probes can be displayed wirelessly in the testo 635 measuring instrument, i.e. data is transmitted by radio. Selectable user profiles, i.e. function buttons allocated to a specified application and menu guide facilitate intuitive operation. Data is transmitted via infrared to the Testo printer. Material moisture can be displayed directly using special probes. The heat transfer coefficient (U-value) is measured using the U-value temperature probe and a radio probe. To analyse humidity on ceilings and walls, testo 635 shows the dewpoint difference between ambient air and wall surface. Precision probes up to -60 °C tpd are available for checking pressure dewpoint in compressed air systems.