To carry out their calculations, merchants in the early 13th century used an abacus or a system called finger reckoning. Commerce changed when Leonardo of Pisa â known today as Fibonacci â published the first arithmetic textbook. Mathematician Keith Devlin talks about the history of arithmetic and his new book "The Man of Numbers: Fibonacci’s Arithmetic Revolution."

http://www.npr.org/2011/08/12/139579620/how-fibonacci-introduced-the-world-to-numbers?ft=1&f=1007