i got one last year from our hardware store and 12 hatches later, it was working fine. I will start my incubator back up again next month....let's hope it's still working good. I always put 2 different ones in there to see how close they are..and do the first hatch like that. Good Luck.
I have bought many over the years both expensive and inexpensive and returned many to the stores in which they were bought until I found one that was correctly calibrated or at least as close as it should be. The link below will tell you how to calibrate you hygrometer. http://exoticpets.about.com/od/herpresources/ss/hygrometer_2.htm