Those analog thermometers can be somewhat inaccurate. I wouldn't trust them. I also think a thermostat is one of the most important pieces of necessary equipment when keeping snakes. I'd recommend getting one ASAP. Those heat mats can get pretty hot if left unregulated. You can also invest in a temp gun so you can monitor the temps anywhere in the enclosure. These are a couple of relatively inexpensive options.

http://www.amazon.com/gp/product/B00...gw_p199_d43_i2

http://www.amazon.com/Nubee-Temperat...words=temp+gun