Product review (1 stars): You get what you pay for  or, in this case, less.
An utterly worthless product based on my experience. This displayed a 20 degree variance in humidity within five minutes  from 12% to 32%  in the exact same spot. It started at 5%, then shot up to 32%, then went back down to 15%, all in the space of a few minutes. Curiously, the actual reading in the room was 41%, when tested against a professional-grade hygrometer. I use these gauges for my acoustic guitars, so I am serious about monitoring the humidity level. I have owned mini humidity monitors in the past that were as cheap as this one and gave accurate readings. This one was a total bust.