What this is
The Inca state kept its counts on cords. A quipu is a main cord with thinner cords hanging from it, and knots tied in the hanging cords record numbers. This page lets you do what the accountants did: read a cord to a number, and tie the knots for a number of your own. Nothing here is scored. Take as long as you like, and tap New cords as often as you like.
The rule of the cord. Where a knot sits tells its place. Knots nearest the main cord count hundreds; knots in the middle band count tens; the knot at the bottom counts ones, and it is a different kind of knot, a long knot whose turns you count. An empty band means zero. So a cord with two knots at the top, no knots in the middle, and a long knot of five turns at the bottom reads 205.
One more thing the accountants knew: a one in the ones place is tied as a figure-eight knot, not a long knot with one turn, because a long knot cannot be tied with one turn. On this page a figure-eight is drawn as a small 8.
1 · Read the cords
Three cords hang from the main cord. Read each one to a number and type it below. Tap Check when you are ready.
Read each cord to a number and write it on the line beneath it.
2 · Tie the knots
Tie this number on the cord. Tap inside a band to add a knot there; tap a knot to remove it. In the ones band, each tap adds one turn to the long knot.
Draw the knots for this number on the blank cord: single knots in the hundreds and tens bands, a long knot with the right number of turns in the ones band.
Tie:
3 · Tie the total
Two cords are already tied. Read them, add them, and tie the total on the third cord. On many real quipus the total cord was tied so that it hung the other way, upward from the main cord, so a reader would know it was a sum and not a third count.
Read the two tied cords, add them, and draw the total on the third cord.
Carrying works on a cord the way it works on paper: if the ones add to more than nine, the extra ten becomes a knot in the tens band.
What the knots do not say
The reading rule on this page comes from Leland Locke, a New York mathematics teacher who worked it out in 1912 from quipus in the American Museum of Natural History, and from Marcia and Robert Ascher, who studied hundreds of quipus in the 1970s and found that many carry a cord holding the total of the others. The numbers, in other words, can be read. What the numbers counted usually cannot: the cords rarely say whether a 205 is people, llamas, or jars of maize. That knowledge lived in the keeper, the quipucamayoc, and was not written down. Some scholars think the colors and the way cords are attached carried more than numbers, and that some quipus held stories; that reading is not settled.
Sources: L. Leland Locke, The Ancient Quipu (American Museum of Natural History, 1923); Marcia Ascher and Robert Ascher, Code of the Quipu (1981); Gary Urton, Signs of the Inka Khipu (2003). The Map wears a photograph of a real quipu, from the Museo Larco in Lima.