Compare the Suan Pan, the Soroban and the Nepohualtzitzin
The Suan Pan
The Chinese abacus, Suan Pan, Circa 1200 A.D.; 5 beads in the lower deck, 2 beads in the upper deck.
The Soroban
The Japanese abacus, Soroban, evolved from the Chinese abacus circa 1500 A.D.; 4 beads in the lower deck, 1 bead in the upper deck.
Aztec abacus
Nepohualtzitzin circa 900-1000 A.D. 3 Beads in the top deck, 4 beads in the bottom.
