This. . . Abacus Abacus is of course a disk used for calculation, hehe. Generally divided into upper and lower, upper two, lower five (for students and accountants, lower four, upper one). From bottom to top, dial a bead up first, and record it as "1". If the two beads on the right dial 2 up, it is 20. If there is only more than one decimal number, it is recorded as "50". If there are all ones on the top and all four on the bottom, it is "99" plus one -99+ 1 = 6550. My primary school math is the worst, but abacus toys are still quite fun, hehe.