Looks like the latest 'Gadget' from Jameco has duplicated an old method, or a variation on a theme.
http://www.jameco.com/z/21-880-Kit-...+Mouse&utm_campaign=FQPROJ&utm_content=FQPROJ
Like..

Max.

 

Thanks Max. A machine like that fascinated me in the 1970's. I had a company flame cut some heavy duty bumper mounts. That is what inspired me to build a CNC plasma table. After writing my own software to follow lines on bitmap pictures, I forgot about edge tracing. That may come in handy.

 

I still have an old LinoTrace head some where, not sure if it is usefull for any thing now in the days of CNC.
They used a very similar principle that the Jameco mouse does, just not quite the same.
Max.