Abacus, also known as _ disk, is a simple calculation tool invented by working people in ancient China, which originated in the Northern Song Dynasty and is an intangible cultural heritage of mankind.

Abacus has different shapes and materials, usually made of wood (or plastic). In its rectangular wooden frame, a string of equal number of calculation beads are arranged, and a beam in the middle divides the bead system into upper and lower parts, and the calculation beads run through the straight column, which has the advantages of convenience and accuracy.

For reference only.