You will want to know the basking spot temp and the over all temp in the cage also your humidity you should know what it is around the top because lower down in the cage will be higher humidity well it is in mine anyway hope that helps ya
Ideally, you'll want to place you temp. and humidity gages in the center/middle of the enclosure. As Kurtis indicated, you want to know your basking spot temp. To make it easy, you'll want to get a temp. gun:
This, or something similar, is ideal for taking random temps. in the enclosure.
A digital humidity gage is a worthwhile investment. I put magnets on mine and that way, I can move it up and down, on all four sides of the cage. This gets me all the different readings from the base of the enclosure to the top of the basking spot.