My training was solely working my way through law school for one of the best finish carpenters that I have ever met. He got me my union ticket, getting me on as a second year apprentice ... and that was working part time. Fit in the mandatory class time as best I could. That was in the seventies. Didn't even pick up a hammer again, until 2006/2007, having only paid dues to keep my journeyman's card.
In any event, Common rafters, piece of cake ... right? I was working with three, count 'em three, journeyman card carrying union members. 8 x 12. Two of them run to their cars/pickups to get their Construction Master Pro calculators (the smart phone apps hadn't quite caught on yet). The other just kind of looked around and mumbled.
I started marking and cutting ... They all asked me how you do dat? I handed them the "little blue book" that used to come with a Swanson's square. TOO funny ... remember these guys had journeyman tickets.
You can't make up this stuff.