Not Stupid by a long shot..... Just learned by error !! ;)
Have a short/mid arm on a frame, prewound a bolt of backing, sounds good right.
Weeellll didn't pre mark estimated yardage before loading the backing fabric and yep 3/4 th thru a Quilt ran out of backing, what a mess, ended up unwinding enough to put regular machine on a rolling cart and adding some more backing fab.
Yep.... now it gets marked, before loading.... Lesson learned!! :)