The floor plan for the Japanese abacus (soroban) is one bead above, four beads below. The floor plan for the Chinese abacus (ch'uan pan) is two beads above, five below.

Um. Well then. I always assumed NEVER ASSUME ANYTHING !! that "abacus" was Chinese word, and that the Japanese "translation" was "soroban." 'Taint so, I see.

Now if the Chinese abacus is a ch'uan pan, and the Japanese abacus is a soroban, then where did the word "abacus," meaning a calculating machine, come from in the first place? Latin, after all?