What temperature do I believe?

The delay in the onset of active fermentation made me question whether my fermenter was too cool. As I noted in previous posts the controller has a pretty wide temperature band to work with, and I worried for a while that it was too cool. Of course it started foaming yesterday so my worries were unfounded but I am still curious about the temperature.

For the purposes of studying this batch I put an additional digital thermometer (the same red one that you see stuck to the propane tank in one of the pictures below) into the chamber to measure ambient air temperature. In addition, my kit came with a stick-on "Fermometer" which has a mood-ring like ability to indicate temperature, so I applied it to the carboy as well. I also got a standard mercury thermometer in the kit, so what the hey, I tossed it in as well.

Here's what I found this morning:

• The digital thermometer reads 73 F
• The Fermometer reads 66 F
  
• The mercury thermometer reads 66 F
• The temperature probe reads 60 F

I expected the probe to be different because its temp changes are buffered by it being in a Mason jar full of water. The Fermometer is reading (I think) directly off the carboy, not ambient, but the mercury thermometer is reading ambient. (I discount the digital thermometer because I have decided it's too cheap to be accurate at low temperatures - it's designed for testing meat on the grill.)

Conclusion: I'm obsessing over this too much.