We have the ND and the regular one. We like them but are having problems keeping the temp constant on them. We set the temperture and it changes constantly by 3-6 degrees. We put a thermometer on each rack to double check the temps and we are having to set the herpstats at 83-86 to get a 93-96 temp. I am thinking we are just not doing something right with the herpstat but can't figure out what. We have the probes for the herpstat 1/4" away from the heat tape and it still wont keep the heat where we need it. This is a problem cause now we have sick snakes do to the temp dropping and us not knowing. I know the herpstat is a good thermostat. I just don't know what we can do to get it to work right so we can trust the temp we set it on and stop this temp changing so more dont get sick. If anyone has the problem or knows what we are doing wrong please help us. Thanks so much....