calculator evolution
TRANSCRIPT
http://www.vintagecalculators.com/html/evolution_of_today_s_calculato.html
http://www.ideafinder.com/history/inventions/handcalculator.htm
http://electronics.howstuffworks.com/gadgets/other-gadgets/calculator1.htm
http://scienceray.com/mathematics/the-history-and-evolution-of-the-calculator/
http://www.youtube.com/watch?v=8dDuZqpp-iU
start with abacus