The abacus is an old calculator with many styles. This app provides both Chinese and Japanese versions. The Chinese abacus has seven beads on a vertical bar, while the Japanese version has five beads on a vertical bar. As a general rule, each bead on the lower deck represents one when moved towards the center beam. Each bead on the top deck represents five when moved to the center beam. In the Japanese abacus, each bar can represent from zero to nine units. On the other hand, the Chinese abacus allows the representation of zero to 15 units in each bar, thus supporting calculation using the base 16 system. For the base 10 system, the two beads at the top and bottom are not used. About the decimal point, users could, in fact, choose their own location depending on their specific needs.