[jesperlang]

I have a similar abacus (japanese soroban) and use it to keep scores in board games by dedicating say three columns per player (they will never get more than 999 points). It is such an underrated piece of "technology". Calculating actions (e.g "add 45", "subtract 13") become finger movements. You can "feel" what the actions represent in finger movement. This enables you to calculate very fast, faster than typing it into a calculator. I am sure the roman calculators (the humans operating the abacus) got really fast at this, maybe even to the point of internalizing a mental abacus. Look at the guy on the left in this counting contest, he's air counting on his mental abacus: https://www.youtube.com/watch?v=F-THPY14fzc

[huytersd]

I don’t think you’re familiar with accounting pre excel. They could type on the numpad at insane speeds, “feeling” the math if you will.

[op00to]

The boy got the answer wrong! But I have seen math schools where the children do similar arithmetic on air abacus. Just this kid couldn’t hack it with those fast digits!