Control and calibrate Testo humidity probes easily: A defined humidity is generated in the two special containers with the aid of saline solutions (11.3 %RH and 75.3 %RH). The humidity probe is screwed into the first measuring chamber for testing and is thus exposed to the defined relative humidity. After an acclimatization time, a stable humidity is reached and the display value of the measuring instrument can be compared with it. The probe is then screwed into the second measuring chamber and the process is repeated.