I just picked up a refractometer thinking it would be easier to take gravity readings during the mash & boil but noticed its ATC feature goes up to the 80s - my question is does that mean I still have to cool the sample or is it easy enough to temperature adj reading?
ATC adjusts for the temp of the refractometer, not the sample. The sample size is so small that it will cool by itself.
From my experience, ATC is useless when cold. I bring my refractometer inside these days and keep it in my pocket on brew day. Without this, my numbers were all over the place.
Yep, same here.
This is such great info, wish I had known this all along. Thanks Steve
+1. I used to store mine in the garage and definitely noticed that. Since I started keeping it inside, readings stabilized a lot.
+1 to what Denny said.
I still cool my sample down a bit before I take a reading but it probably isn’t completely necessary. The time of year I do most of my brewing I usually have a number of inches, to feet, of snow to use as a quick cooling source. 8^)
Paul
When taking hot wort samples, I blow on the refrac for a few seconds before checking it, seems to work fine.
Pour a lot of the boiling wort over it for the initial reading and it is pretty reliable. On the cold side just keep it in your pocket and you should be fine - just my experience…not as problematic as my pH samples which must be cooled to room temp.
Little trick-- get your sample, 2-4 oz, in a plastic cup or something, then submerge the bottom in your sanitizer bucket (I always keep 5 gal of StarSan solution around) and swirl. 70F or less in under a minute 
I use shot glasses for pH samples and keep a small bowl of crushed ice and water handy. It doesn’t take long at all to cool half a shot glass down.
Your refractometer is in heat? Maybe you should get it neutered.
OK, bad joke, but that’s what came to mind when I saw your title. It might have been because their’s a cat on my lap, and I just finished a DIPA.
It was merely a matter of time.