I have all digital thermometers. The heat mats are outside the tanks on the end and I have the probe between the mat and the bottom of the glass that are connected to thermostats. I also have a temp gun and check with that several times a day. The thermostats are at their highest but it's still not high enough when I check with a heat gun. I do find that the heat gun is very close to the temp that I have a probe under the glass in the middle so it leads me to believe it's pretty accurate. Much better than the thermostat.