Yeah, I think we all have learned to start at the one, at some point in our experience. But since the topic is "precision" framing square. I know that's an oxymoron. -)
In any case, I like to have at least one nice L square and one nice rule (from a combination square) that are each sanded "true zero" on each end and at the corners.
I often find myself with a square and a file, taking of the blister from a ding at the corner where it's been dropped on the concrete floor.