Here is the VIII book “Real Comments” written by Garcilaso. Adaptation of a part taken from the chapter on Quipus:
"It was counted through threads and
knots and there was the conviction of the quantifiers. The Indians made threads of various colors, one of a single color, another of two colors, others of three and others of more color. Both simple colors and blends had their meaning. The threads were curved, of three or four strands, as thick as the iron axis of the spinning, with three quarters of length (1,2 m). All of them were cut into another main thread. Depending on the color of each thread they knew what information the thread had, for example, yellow indicated gold, white silver and red warriors.
Some of them had hanging other butchers of the same color; for example, if in a thread were numbered men or women of a certain age — it was considered that they were all married — the aforementioned little baskets gave the number of widows of that age. This type of counts were also performed annually.
The knots of the strings were indicators of different orders, individual, decimal, percentages, thousands, ten thousand, and hardly the knots corresponding to the one hundred thousand, since as each people made their own computation and each capital of their district, the number of inhabitants counted never reached the one hundred thousand. They already had as many numbers as they were. However, although on occasion the amount exceeded one hundred thousand, they would have no problem to count it, since in their language any number can be indicated. To read the number given in each of the threads we had to count the knots overcome by the free end of the thread, the first group corresponded to the individuals and from there appeared major orders. Keep in mind that the knots corresponding to each order were all together, as can be seen in the rope of the Blessed Patriarch of San Francisco."