I own three other hygrometers and all three were easily calibrated. The reads on this hygrometer is way off... I took it to a buddy of mine who works at a cigar shop and asked if MAYBE I was doing something incorrectly. He held onto it overnight to place in his own humi's and sure enough, the read was totally off. Yes, we both tried to adjust it when calibrating it but its just not working correctly. It's a very good chance I just received a dud however at this point I don't recommend this product...