Just go to amazon and type in acurite 00891, which is the probe and what you want. I have 2 different styles of these and they work great and very accurate. They give same reading as my Herpstat and VE thermostats and I have done the salt test for the hygrometer and they are right on. I own 11 of them and lots of people on here use them. You put the probe under substrate on hot side and run wire under the substrate to the cool side and set the unit on the cool side and with one look you can see your hot side temp, cool side temp, and humidity. They have become very popular for reptiles and are actually more accurate then any thermometer labeled for reptiles that I have used.

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