We talked about this over a decade ago. I show you this, not to sell their product, I'm not affiliated, but also, who really needs a manual on this?
But just look over their products.
http://vintageblueprintscashbonanza.com/
And are people REALLY cashing in:
https://www.ebay.com/sch/i.html?_fro...eprints&_sop=3
I don't know, but it should give a few of you some ideas, eh?
Check out these guys:
https://www.patentearth.com/
Gordon