This is based on the binary marble adding machine from this web site and is based on the plans from the site: http://woodgears.ca/marbleadd/ There is also a great YouTube video explaining how to use it: http://youtu.be/GcDshWmhF4A It's a great way of teaching binary numbers and it is also a lot of fun to watch the marbles fall!

This is designed to be laser cut in 5mm (1/4" nominal) plywood and then all glued 3 thick for the bars, and the rocker mechanisms.
Follow the assembly directions from http://woodgears.ca/marbleadd/ but save oodles of time by cutting this on a laser cutter instead of by hand.