Counting on the Inca’s quipu, their ancient string counting device, is easy. Each hanging string represents a number. They used a base-10 system like ours, with the bottom group of knots being the ones (1 knot = 1, 3 knots = 3, 9 knots = 9), the next grouping above being the tens (3 knots = 30, 5 knots = 50), the next highest being the hundreds (3 knots = 300, 5 knots = 500), and so on. A zero in, say, the ‘202’ pictured below is represented by a space, or no knots, where the tens would be. An Inca accountant, who was specially trained, would do addition and subtraction during the trading of goods or inventory by tying and untying knots on his quipu. The strings were often colored coded. For example, the knots/number on a gold colored string might represent the amount of gold they had. In Inca court, an accountant’s quipu was considered legal documentation.