During what scholars call the modern Horizon period, approximately 600-1000A.D on the European timeline. The Incas employed a device called the Quipu or khipu. Thedevice consists of a series of cotton cords. There is a main cord from which from which many "pendant" cords hang.
While Quipus seemed to be a general data bearing device (for instance colors of cords were used to represent different materials and states of affairs), one well-documented use was to represent quantities and calculate numbers. Knots in the pendant cords and their relative position on the cord allowed the Incas to represent numbers using a decimal system (1s, 10s, 100s, etc..).
To perform a calculation like adding one can count knots across cords, carrying sums upward and recording the total on a separate cord.
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