^ This, re: temp to use. One way to think about it is ... well, it's chemistry. Physics, maybe. Yeast produces CO2 during ferment, which some bubbles out but some dissolves in the beer on the way. How much depends on pressure and temp, for a given beer. So if you ferment at 68°F that determines what will dissolve into solution. If you bring it up from the bowels of your fermentation dungeon to bottle in the parlor, and it spends a few hours there while you're composing a sonnet, some CO2 will come out of solution. But generally speaking, you use the ferm temp. Those who cold crash would not use the cold temp for priming calc, as that was not the temp during which active CO2 was produced to go into solution. Make sense?