2 hides one on the cool side & one on the warm side. The UTH MUST be controlled by a thermostat (to regulate temps - so dont burns happen) or at least a rheostat (dimmer). An uncontrolled UTH can reach temps of 120 degrees or more. You need to get something to control it ASAP.
Hope this helps.
*EDIT* also you will need a digital thermometer with a probe so you will know what the temps are. Place the probe over the UTH inside the tank. Sorry almost forgot to mention that.
You can pick up an inexpensive one at WalMart for around $12 (I believe the brand is Accurite) These also measure humidity so you won't need to purchase an additional digital hygrometer (sp??)