I have always used the traditional thermometers with a suction cup in my display tank and they always seemed to perform well.
I bought a digital thermometer (lifeguard) today and put it in my sump and it giving me a totally different reading 83.3 as opposed to 80 from the old thermometer. Logic would say that the one in the tank would give a slightly higher reading due to it being under the lights (PC). I have the digital one away from my heater (250W Ebo Jager) and I dont fully trust it.

Do you find these digital thermometers to be accurate? Do you set yours up in your sump? or in the main tank?

On a different note....These Ebo jagers dont seem to maintain a temp I set it at. (If in fact the digital one is accurate)