SuanPan Abacus

thingiverse

The top pair of beads symbolize a value of five each, and the bottom set of five beads represents one collective unit. You simply tally up the number of beads adjacent to the center units. The dimensions are 8 inches by 7 inches. I apologize for any confusion in the photo quality, as I was operating under time constraints, but this illustration should convey the concept.