Mend the Khipu

This khipu has four groups of four cords. Above each group rises a top cord, tied through the loops of the four, which holds their sum: Leland Locke found khipus like this at Huando, on the coast of Peru, and the sums were how he proved the knots were numbers.

Some knots have worn away: their places are marked with dashes. Read the cords that survive (the ones farthest from the main cord as a long knot, the higher places as clusters of single knots), work out from the sum what each worn place held, and tie it back: tap the worn place to tie a knot, tap the − to untie one. A worn place you leave empty counts as zero. Each group has only one answer, and you can make three mistakes. New to khipus? Start with Knot Count. The game is a draft and not yet checked.