Inca quipu counting device. Artwork of part of an Inca quipu (also spelt khipu). This counting device was used by the Inca people of South America in the 15th and 16th centuries. It consists of a series of coloured strings attached to a base rope. These strings were knotted to encode numerical information, arranged in columns of numbers. The colour of the strings signify the objects being counted. The quipu could be used to perform simple mathematical and arithmetic calculations, and has been described as a primitive computer.