[bluemetal]

For number 115: by moving the bigger piece side to side you spin the two wheels. Each wheel spins the same amount but in opposite directions. Shafts attached to those wheels can be used to drive components that need to move equally but in different directions.

[hfsktr]

Perfect! I couldn't have even visualized that. I just saw gears and didn't even think about a rod off that.

Another thing that would be interesting is to know when some of these came about (some are older than people might think [1]).

[1] http://en.wikipedia.org/wiki/Odometer#Ancient_China