For the sake of simplicity, my use here of number words (ten, hundred) instead of digits (10, 100) will refer to decimal values. "Ten" =
I've been interested in arithmetic on the abacus for a while now, although I'm still quite the amateur. Last year I wrote a (not yet officially adopted) plugin to the Khan Academy Exercises engine to allow practice exercises on a 4x1 soroban, which helped me improve my speed and accuracy with basic addition, and I've acquired these two real-world abaci:
The top abacus is a cheap Chinese 5x2 Suanpan I bought in Chicago's Chinatown a few years back when my wife and I vacationed there, and the bottom abacus is a better quality Japanese 4x1 Soroban that Liberty ordered for me as a Christmas present last year (along with a book on the Haskell programming language I've been wanting - best wife ever!). "Suanpan" and "Soroban" are language variants on the same word, which roughly translates to English as "counting tray", and neither name implies a specific number of beads.