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Gerbert devised a new kind of abacus which one could use to calculate with the Hindu numerals, a flat board with columns drawn on it, corresponding to ones, tens, hundreds, and so forth. (Some scholars believe he may have been the first person to use the Latin term *abacus*.) He had a shield-maker construct small pieces of animal horn with the numerals on them; called *apices*, the pieces could then be placed on the board to represent numbers. A zero was not necessary; the absence of a marker in the tens’ place, for instance, meant that there were no tens. An eleventh-century manuscript found in Limoges illustrates the representation of numbers on such an abacus. (Note that the numerals had changed slightly in the next hundred years.)

Gerbert compiled a list of rules for computing with his abacus, *Regula de Abaco Computi*, in which he painstakingly explained how to multiply and divide, as well as add and subtract, in the new system. A companion work, *Liber Abaci*, by his student Bernelin, is often included in the collected works of Gerbert; it predates the book of the same name by Fibonacci by two hundred years.

To see an example of how to add numbers using Gerbert’s abacus, click here. [This is a power point animation of the process.]

And for an example of subtraction, click here.

Betty Mayfield, "Gerbert d'Aurillac and the March of Spain: A Convergence of Cultures - Gerbert's Abacus," *Loci* (August 2010)