There are several different models of Acurite thermometer/hygrometers. You'll find at least one at your local Walmart, typically near the garden section. Just be sure you purchase the indoor/outdoor thermometer with humidity. There are not two probes to these units. There is one probe which measures the "outdoor" temperature, or in this case the temperature of the glass directly above your UTH. Then there is the unit itself that measure the "indoor" temperature and humidity, in this case the ambient temperature and relative humidity. The unit itself is placed on the cool side of the tank. They're cheap and easy to use.
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