ran across this thing in a friend's garage, took a while to do some research, but if you follow the link below to the ebay auction, I have a link there to the relevant patent (you need to have the proper viewer installed to see it) - the text that goes with the patent is very interesting in that it explains all the key considerations for this guide.
I have never seen another, but then again, I'm not much of a tool collector - what about you guys?