The traditional Inca quipus were numbers expressed by knots on a section of rope. Unlike the Arabic numbers which uses ten different symbols for each digit (0 to 9), quipu makers tied multiple knots in a tight sequence represent a "digit". Digits can range from no knots (empty space) representing zero, to nine knots representing nine. Seven knots in a sequence equals the digit 7. A quipu could have only a few or up to 2,000 cords.