Temperature/humidity measuring instruments such as the Wallac Thermohygrometer EP-400 Temperature/Humidity Instrument (LC-400/05 air probe) utilize the change in electrical resistance of an electrolytic film to measure humidity and rely on a sensing or measuring probe to detect this change. A problem with instruments of this type is that the current flow from the electrical measuring circuit through the probe sensor causes selfheating of the sensor which affects the reading (an increase in the reading of 1.degree.-2.degree. C. above ambient has been noted with the Wallac thermohygrometer). To combat this problem, it is suggested by the manufacturers of these instruments that the probe be swung back and forth evenly to create air flow (at least 0.5 meter/sec. in the Wallac thermohygrometer) so as to cancel the self-heating effect. However, tests have shown that this approach is less than satisfactory from a number of standpoints. Chief among these is the fact that swinging of the probes does not provide a steady constant air flow and thus does not produce reliable readings. Other problems which affect performance include the amount of time necessary to achieve stable readings, the lack of uniformity in swinging techniques and the difficulty in ascertaining when a final balance is reached.