Frustrated With Temperature Readings

[viperfish]

After getting varying readings in several digital thermometers from Marina, I decided too take the plunge and spend some decent money on a Pinpoint wireless thermometer. I have two sensors set up, one in my 180 and one in my 90. I'm beginning to think there isn't an accurate thermometer out there because my Pinpoint is telling me my 90 Gal tank is at 81.3 and after trying every thermometer in the house I honestly believe it is between 78 and 79 which is what I want. It is also telling me my 180 is at 79.9 when I think it is at around 76. All I want is an accurate thermometer, anyone know where I can get one? Anyone have troubles with the Pinpoint? Between all the crappy heaters and crappy thermometers out there, it gets very difficult to control temperature sometimes.