I have a similar one:
http://www.cheaphumidors.com/p_cabin..._HUM-1000.html, and I really like it, but for some reason the humidity on the bottom is different than the top, always. I tried different things to no avail. Sometimes as much as a 6 percent difference, but right now only 2 percent. 66 and 64. My endtable humidor (antietam) is smaller but has no fluctuations.