From Wikibooks
< Abacus‎ | Manual

There is at least one row of an abacus and up to as many can fit in the box. The first row stand for the first digit for example 1-10. The next row up stands for an extra digit meaning that the next row stands for 10-100. Once you fill up a row, like that the entire row is moved to the right, then you move a bead to the right on the next row.