http://www.ideafinder.com/history/inventions/abacus.htm The Abacus idfnd ideafinder.com idfnd the Idea-finder http://www.ideafinder.com/history/inventions/abacus.htm http://www.ideafinder.com/history/inventions/abacus.htm A History: Invention of the Abacus Abacus History - Invention of the Abacus