LionJim (and other math geeks).....a mystery for you (link)

[Michael.Felli]

http://www.npr.org/2015/06/23/41461...eserve-newly-discovered-chalkboards-from-1917

I can't figure out the wheel.

 

[sluggo72]

http://www.npr.org/2015/06/23/41461...eserve-newly-discovered-chalkboards-from-1917

I can't figure out the wheel.

if you hit the links, you find an explanation. basically it was a training tool. No magic here, just plain old wrote memory.