When I first received this hygrometer, I was convinced it was a piece of crap. The temperature and humidity readings were inconsistent and laughable. I tried to calibrate the unit numerous times before I finally gave up and forgot about it. I procrastinated long enough that sending it back was no longer an option. Finding the thing in the bottom of the junk drawer, I was ready to toss it but instead swapped out the batteries for fresh ones (it pays to buy those variety packs!). Lo and behold, the temperature reading was accurate and steady. After 48 hours in a bag with saturated salt, it read 75% RH. A day in the humidor gave a reading of 65%, matching the humidity beads.
The lesson learned is to check the batteries before tossing aside. Accuracy is lost with any battery weakness and this unit seems to be especially sensitive. That is a good thing...right?
The calibration feature truly puts the mind at ease. Don't bother with any calibration kits, google the procedure for simple instructions after buying this hygrometer.