I'd recommend to the original poster and everyone else to consider
water flow around the heater (I think netmax recommended this) and the
thermometer as well. I mistakingly attached my lcd thermometers to a
place as low on the tanks as possible without touching the bottom
plastic rim to keep the thermometer out of the way and I experience
temperature fluctuations on all of them I think because of that. There
is gravel substrate on the other side (i.e. in the tank) and I think it
prevents accurate readings and I am using all ebo jagers which are
rated as having a temperature fluctuation (on the box it came in) of .5
degrees fahrenheit and in the manual (or vice versa) a fluctuation of
..5 degrees celsius. My heaters generally have good water flow around
them though. I think the cause of the fluctuations in my case is
inadequate water flow around the thermometers. I have temperature
fluctuations of approximately 4-5 degrees at times either above or
below what I have the heater set to as far as temperature goes. I tend
to trust the heater's temperature dial more than the thermometer but I
keep both in mind and keep the temperature setting on the heater in
range with the creature's requirements and read the thermometer keeping
the accuracy in mind and seems an acceptable solution at the very least
for now. Later!