Knot Count

A khipu is a main cord with cords hanging from it. Each hanging cord holds a number in knots, counted in tens like ours: the ones farthest from the main cord, then the tens, hundreds and thousands nearest it. No place has more than nine knots, and an empty place is a zero.

On the khipus Leland Locke studied in 1912, from Huando on the coast of Peru, the ones are a long knot, wound once for each unit; a single ordinary knot means one. The higher places are clusters of single knots. A top cord, tied through the loops of a group of cords, holds their sum.

Each day has five cords. Read three: tap the number you see. Then tie two: tap a place on the cord to tie a knot there, and tap the − beside it to untie one. The game is a draft and not yet checked.