Tie a number. Take a long piece of string and tie it to a pencil, so it hangs down. Tie knots in groups: high up for tens, near the bottom for ones. Leave a gap where there is a zero. Swap strings and read each other's numbers.

Before chapter 3. Beto counts 14 knots on the first cord. What is the cord really saying?

The answer. 347. Three knots high up are hundreds, four in the middle are tens, and a long knot of seven turns is ones. Where a knot sits tells you what it is worth. The thick top cord read 682, the total of the cords below: 347 + 125 + 210 = 682.

The honest part. Nobody knows yet whether some khipu recorded words or stories as well as numbers. Researchers are still working on it.

The grown-up layer. Place value is the reason we can write a big number with only a few digits. CarryPals has Loaf, who squishes ten ones into a ten.

For the ride home. Ask: how would you tie the number 105?