Very interesting tool Jim. It executed well, it may be worth having certainly. The trouble is often finding a square that is actually square. I have two Japanese squares from Lee Valley which seem pretty good. It sounds like you could make two brackets, one that bolts the two squares together, and one that holds a combination rule to a square. This would allow the TF'R to use his their existing squares and combination rule. That would be a good thing. You know, I have over half a dozen prototype parts/machining jobs that I need done, but don't know any machinist to give the jobs to. Some don't want small jobs, but mine add up to a decent amount and they could use it as filler work - If I could find someone up to snuff. That's the hard part.
Do you know how it(the bearing face measurement) would have been done say 150 years ago?