Exactly but very slowly

Under 10 minutes (minimum!) You can not trust a reading. This makes the device impractical to measure to different rooms. In my comparison tests with an accurate temperature sensor PT 1000 I was able to reach room temperature after 20 minutes a deviation of about 1 ° C at 25 ° C. Overnight, then the measured value of the Testo possible device on + - 0.1 ° C. Since the relative humidity depends on the temperature, the device displays when the temperature changes only times at very unrealistic values ​​for moisture.
Conclusion: In rooms whose temperature hardly varies suitable. To once just the temperature and humidity measuring unsuitable immediately after airing, because you have to wait too long. The final accuracy of the moisture measurement, I could not judge, since I had no comparison to device.