Real pots of liquid do not heat uniformly like they do in the physics textbook equations. "A very slow boil" does _not_ mean the _entire_ mass of liquid is nea

Real pots of liquid do not heat uniformly like they do in the physics textbook equations. "A very slow boil" does _not_ mean the _entire_ mass of liquid is near 212 F. It means that _one very small sector_ of the liquid is near 212 (hence the 'bubble at one point'), and the vast majority of the liquid is considerably colder. A thermometer is unnecessary.