Product review (5 stars): Wonderful deal for the price
I read the negative reviews posted about these things being off on accuracy, so the first thing I did when I got them was put in new batteries and place them all next to each other on the coffee table. I let them set there for about 15 minutes before reading them, to give them time to adjust ffrom being in a box. For a set of four, there was a total variance of 2 degrees on the thermometer (from highest reading to lowest), and 5% on the humidity gauge (from highest to lowest). I have noticed some weird fluctuations on one of the units, going back and forth from 50% humidity to 54% humidity in a matter of less than a minute. This was mostly frustrating because I kept thinking I'd misread it - repeatedly - seeing as how it did this for about 20 minutes.

Are they 100% accurate? Of course not. But they're also affordable and accurate enough for monitoring the library and bedrooms in my house.