Towing Calcualtor - Not having to look up truck ratings

Funny thing, I worked at the plant where they make the GM HD's....2500, 3500, and never saw where they were weighed to get that door sticker. Hummmm......I saw everything else about the manufacture of these vehicles from frame, axles, box, cab and engines but never saw where there was a scale to weigh each and every one of them. I never thought about it.