The old man whom I started with almost 30 years ago, if I would have been using a marker on the sheetmetal(thats what awls are for) and would have not clipped the corners-He would have hit me upside the head with that piece........
I guess if you have to field fab something Magic Marker is ok.
The old codger who taught me didn't have patiance for BS either.
when I screwed something up he'd stab the scratch awl between my fingers.
Lucky for me this guy had a precision eye. But that was what the lesson was about, if he hadn't had a good eye he would never have pulled that stunt.
Shesh..everybody who's somebody in sheet metal had a "Mr. Miagai" type instructor.