Product review (2 stars): I bought three of these hygrometers. The first thing ...
I bought three of these hygrometers. The first thing I did was set them side by side in one room and let them acclimate for 24 hours. The readings ranged from 15% rh to 27% rh. They never equalized.  Even the temp readings  varied but were closer together. I guess you get what you pay for.