When I was in cooking school, it was assumed we would not have the time or equipment to constantly be monitoring temps with a thermometer so we had techniques for determining fairly precisely the temp of things.
Poaching liquid was evaluated based on the quantity and rate of bubbles rising from the bottom of the pan.
Milk was scalded (e.g. for bechemel) when the milk foamed but was shut off before it boiled over.
A knife inserted in a steak, chop, or roast could be tested for temp against your lower lip or wrist (yes, yes, hygiene and so forth).
The techniques you are talking about all came about because of all understanding of food that led to science asking "why does cheese happen the way it does". The precise techniques leading to a sharp, hard cheese or a soft, fresh cheese were well understood long before instant read thermometers.
Poaching liquid was evaluated based on the quantity and rate of bubbles rising from the bottom of the pan.
Milk was scalded (e.g. for bechemel) when the milk foamed but was shut off before it boiled over.
A knife inserted in a steak, chop, or roast could be tested for temp against your lower lip or wrist (yes, yes, hygiene and so forth).
The techniques you are talking about all came about because of all understanding of food that led to science asking "why does cheese happen the way it does". The precise techniques leading to a sharp, hard cheese or a soft, fresh cheese were well understood long before instant read thermometers.