I bought 1.5 dozen of them and all but 3 were within 1% RH of my calibrated caliber one. All still true after 2 months. I have read that they can be tweaked to proper RH value but have not tried it. Here is a clip I saved from another forum somewhere.
"Sure, I bought a dozen of them.
Cheap is cheap.
However, I also have 6 Caliber IIIs.
So, I put them all in a box and waited.
When they had stabilized, the Calber's all agreed within 1%.
The cheapies were all over the ball park.
But, calibration is easy.
Poke a toothpick through the holes in the back and nudge the assembly until it matches the rest.
Put 'em back in da box until the RH changes and check again.
Only had to discard 3 of them.
I start a jar with the Caliber, then drop in a cheapy for long term storage and save my.
Calibers for measuring where it matters most.
HERE is another on testing and calibration of proper RV setting.
http://www.wikihow.com/Test-a-Hygrometer
Cheers hope this helps.
