Abacus

Abacus, or counting frame, ancient calculating instrument still widely used in Asia. It consists of a wooden frame containing a series of parallel rods strung with beads and divided into upper and lower portions. Each of the rods represents a power of 10; each of the beads on the lower portion counts for a power of 1 and the 2 on the upper portion for a power of 5 apiece. It can be used to solve addition, subtraction, multiplication, and division problems.