Is the thermometer digital or analog? Either way, it won't do you any good to measure the temps at the top of the tank. You want to measure the temperature where the snake is actually at (ground). The dial thermometers aren't very accurate so a digital style thermometer with a probe will be much better for you to get an idea.
Reading a care sheet will do you a lot of good.
http://ball-pythons.net/forums/showt...s%29-Caresheet
Something else to get you on the right track. Very easy to follow
http://ball-pythons.net/forums/showt...-With-Pictures!