Do you know Soroban? It is the Japanese abacus or a traditional handy computer.
The origin of Abacus is not clear according to the Wikipedia, but in Japan the oldest Soroban found may be of the year 1444, 572 years ago.
This is the laboratory of Soroban in Kagoshima, handicrafted.
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Traditional type with 5 beads of earth and 2 beads of heaven, used until Meiji or Taisho era.
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Abacus is absolutely good to develop your brain, it is exported from Japan and opening several schools abroad. This is a text book of soroban in english.
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You can count million, billion, trillion, much more than calculator.
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Do you want to try these calculations?
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Now soroban competion also in English.
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In Hotel Kanyo it is open a soroban class 3 times weekly.

Phew, very difficult.
Sergio.

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