An indoor/outdoor thermometer has a probe that measures the outdoor temp. That probe goes inbetween the glass and the uth or on top of the glass under the substrate. The unit goes on the wall at the the other end of the tank and that will give you the indoor(cool side) temp and the humidity! You will need a dimmer or thermostat on the uth so you can control temps. The warm side should be 90-94 and the cool side should be 80-84. The air temp should be at least 75!