Abacus! Abacus comes from the Greek word ABAX meaning "Calculating Board" OR "Calculating Table". Long time ago people would calculate using sand and little rocks. This might not seem an appropriate word to describe "today's" abacus device. Next generation of abacus became a set of beads on strings in the wooden frame that was invented in China about 700 years ago, during the Yuan Dynasty. So that Chinese Abacus is most popular of all Abacus variations. The abacus was so successful that it's use spread from China to many other countries. It was handy as it could be held and carried around easily. Believe or not, but abacus is still used in some countries. In countries like Russia and India abacus was slightly different but the principle was the same. In some other countries Abacus has different spelling, such as Abakus, abackus, Abax, but in most countries it is spelled as Abacus. That is a little history about abacus, which was today replaced with electronic calculator.

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More details on how to use abacus could be found on Ryerson site, created with JavaScript. Another useful page to learn how to calculate with abacus is Math Mojo.