The HMI41 indicator and HMP42 probes are fully calibrated at the factory, sothere should be no immediate need for re-calibration. Calibration should be performed only if there is a strong reason to believe that the adjustments havechanged. Humidity calibration of the HMP42 probe is done by adjusting trimmerpotentiometers. The potentiometers are located under a protective plug. Thepotentiometer marked T (temperature) is for factory use only; DO NOT makeany adjustments. To make sure that this potentiometer is not accidentallytouched when adjusting the other two, turn the plastic plug aside withoutremoving it completely (see Figure 5.2.1). For adjusting the potentiometers, use a trimming wrench provided with theprobe, or some other suitable tool, e.g. a ceramic 1.5 mm slot screwdriver.