Inside vs. Outside Carboy Temps

I know there are a range of thoughts on this, so I'm just looking for some insight/discussion on how folk's approach this.

I'm 10 days into my first fermentation in my new SOF chiller. I had been using ice in a water bath but wanted something more precise/controllable (and I needed a project). I've got a porter with wyeast 1028 that's just wrapping up fermentation at 62 degrees (measured via probe on the outside of better bottle, covered by a folded towel). I took a gravity sample today and after only a few (2-3) minutes sitting in the hydro tube it read 68. Granted its hot as s%!t in my apartment this week and the sample probably warmed a bit, it got me thinking about temp differential between a thermometer on the outside of the carboy vs. the actual beer temp inside.

I know fermentation is exothermic so there's likely to be some difference, but it seems like 10 days in a 62 environment should bring the liquid pretty close to that temp too. Has anyone done any experimentation on the actual difference in measurement for a thermometer on the outside of a carboy vs. inside? If you want to ferment at say 65, do you just set your temp controller to 65 and forget it, or do you set it a few degrees lower to anticipate heat coming from inside the carboy?

Cheers

 

Anyone? Bueller?

 

There's some good information in the "Similar Threads" down there. VV

 

Sigh. Amateur oversight.

Much obliged.

 

Short answer: yes, and there wasn't much difference.

 

I have a belgian wit fermenting using Wyeast 3944, first time using my chest freezer for fermentation temp control. So far the biggest difference I've seen between the glass temp and inside carboy has been about 1*F.

Brian