DeFelsko PosiTector DPM v.1.2 - Manual (Page 14)

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When the surface temperature probe is not on a surface, Air
Temperature and Surface Temperature appear to be different:
Under normal conditions with the surface probe in air
Ta and Ts should be within the combined tolerance of each
sensor. (Typically 1°C) It is possible for the difference to be
larger if the surface probe has recently been in contact with
surfaces that are at a different temperature than air.
RH value is slow to stabilize:
If the probe is exposed to a very low humidity for an
extended time period and then placed in a high humidity
environment the displayed Relative Humidity (RH) may
appear to respond slowly. Allow the probe to stabilize 30
minutes for a change of RH greater than 50%. It may take
longer if the probe was left at low RH for several months.
To increase response time soak the sensor in a wet face
cloth overnight to recondition the RH sensor.
RH reads much higher than ambient Relative Humidity:
Condensation may appear on the RH sensor when the
probe has been exposed to a cold environment then
brought into a warm environment. Use the 'DRY SENSOR'
option from the SETUP menu to warm the sensor.
Operation of the probe should return to normal.
Surface Temperature reads much higher than expected:
The probe tip may be dirty or damaged. Clean the probe tip
by soaking in water or solvent. Be sure to only soak the
Stainless Steel components of the probe tip. If Ts continues
to read high then return the probe for service.
Surface temperature reported by probe does not agree with expected
surface temperature or surface temperature probe is slow to
respond:
In some cases the surface being measured is very rough
and a good thermal connection from the probe tip to the
surface is not possible. If possible place a small drop of
water on the surface and then place the probe tip into the
water drop. Extremely quick and accurate results can be
obtained in this manner.