I would take a trip to WalMart and look in the outdoor thermometer/air conditioning section. There you will find an Acu-Rite Indoor/Outdoor Digital Thermometer/hygrometer combo unit w/probe. It will run about $15, and is a must have for all snake owners. The analog thermometers/hygrometers are notoriously inaccurate and you could be cooking or freezing your snake and not know it.

I place the unit on the floor of the cool side, laing flat, and rub the probe over to the warm side hide, place underneath warm hide. The unit will measure cool and warm side temps, plus the relative humidity of your enclosure.