Product review (2 stars): Not precise, questionable accuracy
This unit has a handy design and operation however it is not at all precise and I seriously question the accuracy. The most accurate way to measure RH is to measure the wet bulb and dry bulb temperatures. The difference directly correlates to RH (the closer the temperatures the higher the RH). Alternatively, this device uses a capacitive humidity sensor and (dry) temperature sensor to calculate the wet bulb temperature. This is the same method some of the nicer thermostats use as well as accu-rite type units. Hardly worth the money. I bought 2 of these units. One was 13% and the other was 7% higher than several reference devices that all agree with each other.