It's a deterministic finite automaton (state machine) for dividing by seven. In effect, it's the graph expansion of a regular expression.

http://blog.vkistudios.com/index.cfm/2008/12/30/Regular-Expr...

By the way, at http://slexy.org/view/s2QFWeNxZo is a (horrible) regular expression you can pop into "grep -xe" to test decimal numbers for divisibility by 7. (Found with a Haskell programm I wrote via conversion from the DFA.)