Product review (2 stars): No calibration ability?
Purchased this unit from Amazon and thought that all these units were able to be calibrated.  So I purchased a one-step calibration Humidipak.  After placing the unit in the pack for 24 hours, the reading was off by +3%.  Went to the PlanetWaves website searching the instructions and their site on how to calibrate - nothing.  Apparently there is no way to calibrate it and there is nowhere in the limited instructions, where it states it is not able to be calibrated.
Oh well, I should of read the reviews further.  For now I'll just subtract 3% from whatever the reading is.  Otherwise the unit does what it says it does.