You mean a thermometer?
OP, since it seems you're not as experienced in husbandry, I would strongly advise against using a lamp dimmer to control your temperatures. They don't regulate the temperature, they simply provide a steady wattage to whatever appliance is plugged into them. This means that if your ambient room temperature were to rise significantly (i.e. right now, in the transition from spring to summer weather) the enclosure temperature could hypothetically rise from 88 to 98- a dangerous situation. A thermostat regulates the temperature, which is much more reliable and you can 'set it and forget it'. Not the case with the dimmer.
http://www.amazon.com/Hydrofarm-MTPR.../dp/B000NZZG3S
This is the most inexpensive thermostat that is widely accepted as a serviceable unit, and will do a much better job ensuring the safety of your pet against burns. Herpstat thermostats by Spyder Robotics are the golden standard, and if you are able to afford it you should absolutely invest in one.
The thermostat is NOT the component of your setup to save a few bucks on.









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