Temperature Concerns

[Seriak]

Alright, I just bought a Ebo Jager 250 Watt heater and I set it at 27.

Now here is one question.

1) Is this supposed to mean my tank should stay at 27 C or 80.6 F

Now onto the another matter. I have four different temperature reading devices. They each read the following.

1) Crappy hagen sticker reader - 78ish F

2) Standard thermometer 1 year old - 79ish F

3) Standard thermometer 3 months old - 79ish F

4) Digital (Big Display) Monitor with Probe - 77.2 F

They are all placed right next to each other. Why would they all display different results.

NOW THE BIG QUESTION. Which one do I go by? I don't like not knowing my actual temperature. I am sure I could just keep it at a safe level and who really cares what the temperature is as long as it doesn't fluctuate. But this is driving me crazy, I tell ya!

Help.