How South American Incas kept records by the use of knots.

Transcript -- Recording sales in clay tablets

Since the dawn of civilisation, humans have used everyday materials to create mathematical models of the world around them. This album explores the ancient Greeks' astrolabe as a model of the skies; the sundial, to tell the time; Babylonian clay tablets to record wages and trading of sheep; wooden tallies for bulk-buying beer, the Incas' use of knots and string, and the sophisticated number-engine invented by Charles Babbage. This material forms part of The Open University course MST121 Using mathematics.

Incas and their knots