As inspired by this previous question, is there a method or device used to measure the output of a single HVAC vent or the output of a single room?
I'm imagining some sort of hood device that could be taped or magnetically sealed to a vent that would have a CFM (cubic feet per minute) meter on it to make sure each vent is putting out a certain amount. Just to make up numbers, you could then verify that a 6" vent was putting out 1000CFM, and the 8" duct in the next room was putting out 1300CFM, but a 6" vent in the guest room was only putting out 500CFM.
If such a device doesn't exist, how do installers verify that each vent is working as designed? Is it just a matter of a temperature sensor and the fact that the air coming out "feels like the right amount"? How would the poster of the linked question "prove" that one vent wasn't putting out a sufficient volume of air for the room?