Ok there's your problem. Those dial ones are CRAP! Go to wal-Mart and get yourself two Acurite digital thermo/hygrometers
They look like this http://willowtreehome.com/Home-Decor/00891A1.html
Put one side on the hot side and the probe on the cool side on the ground. That will give you a more accurate humidity and two sided reading.
I love my job!!! I really enjoy helping people fully enjoy their Herp pets. Thats why we're here.