I learned how to operate a soroban on Okinawa in 1969. It was interesting watching ta sale in a store. The customer would carry her purchases to the counter. Both the clerk and the customer would produce their sorobans and put them opposite each other on the counter. Each would add up the merchandise on the beads then present the result for approval to the other. If the two devices agreed the total was rung up on the cash register and the sale was completed. If they did not agree then they did it all over again, this time one item at a time while speaking the prices.
Cool! Technology in the assistance of intelligence, dexterity, honesty in business!