Here's a picture of the AcuRite brand that is sold at Walmart for about $12. Since this one gives both the basking & cool side temp at the same time, like beardie parents said, you lay the probe end so that it is resting on the basking surface with the thermometer part on the cool side, wait about 45 min for the temp to stop rising and the "out" reading will be for the basking & the "in" reading for the cool side. If you get a digital with probe with only 1 readout, it would cost about $8.00 but you would have to test each side separately waiting about 45 min each time & moving the probe from the basking to the cool side. The $12.00 one also has a humidity readout. You should find these thermometers in the area where the plastic outdoor thermometers are sold.