Yes, you NEED a thermostat...especially with UTH pads and flexwatt. What only feels 'rather warm' to your hand could actually be 98-110 which is WAY too hot for the snake!

To determine the temps of the pad, you place the probe of your thermometer (which gives the "out" temp) right on the bottom of the tub over the pad. That is the reading you want to get.

When you get a thermoSTAT to control the pad - anything from a top end Herpstat for $110, to a good Johnson for $80, to a cheap but good enough ZooMed ReptiTemp for $25 - you will tape the probe of the stat directly to the heat pad or flexwatt Under the tub, then plug the heat source into the stat. Using the readings of your thermoMeter, you 'tweak' the settings on the t-stat until you have the desired temps.

Sorry if that was confusing...