Product review (4 stars): Indoor humidity indicator with temperature
Compact device. Runs on two AAA cells. Mainly is a humidity indicator with temp as a secondary function. Thus the larger, central number is the humidity and the smaller, lower number is the temp.

The description says is can be "calibrated" ... true ... but it fails to mention that in order to do that you need an external reference. When you enter "calibration mode" you are able to adjust the values up or down to match your standard, accurate source. Without that source the calibration feature is useless.