My Acu-rite is giving me temp readings that are up to 20 degrees different for 2 places that are about 20 inches apart, and with mostly open air between them. Neither the probe nor the main device is under a hide, or behind anything else that might make it a sheltered spot where I might expect such a significantly different temperature.

My tank is a 20 gallon glass tank with a screen top. A piece of styrofoam like stuff is setting on the screen and covers most of it to insulate and trap the humidity. We are using a UTH for heat. It is connected to a rheostat to enable us to fine tune the temps. We have the $12 digital Acu-rite that gives temp, humidity, and another temp from the probe. When I checked the gauge a few minutes ago, it read 90.9 warm side, and only 70.9 on the cool side! Humidity is 44%.

I know 70.9 is too cold. That isn't my question. I'm wondering if I need to figure out a way to add a little heat to the cold side preferably without totally changing my set-up and buying more stuff, or is it more likely that I have a faulty Acu-rite?

We did notice when we first installed the battery that even when we put the probe right beside the main unit, the probe consistently read about 2 degrees cooler than the main unit. We weren't terribly worried about it since I have heard that the digital gauges are accurate within 2 degrees. But now that we are getting such a big difference within the open area of a fairly small enclosure, I'm wondering if the whole thing is messed up.

Any thoughts?