That's sort of what I originally thought. A boil physically cannot be hotter than 212. Then why do I get different results with my analog thermo? At a 212 reading, I have a gentle boil, but I can crank my flame up for a vigorous boil, and then get a 215 to 220 reading. I do calibrate my thermo to ice water before I brew. Is my thermo just not accurate or am I missing something here?