A device invented to assist in arithmetic calculation. It consists of columns of sliding beads mounted in a frame.Just as in the decimal number system, each column defines place value and stands for units (1, 2, ... 9), tens (10, 20, ... 90), hundreds (100, 200, ... 900), and so on when counting from right to left. Beads are slid to the top of each column to represent the digits in that particular decimal place. The number 321, for example, would be entered by sliding one bead on the first column to the left, two beads on the second column, and three beads on the third column.

Today, abaci are still used for calculating in many parts of the world. They are very reliable (they don´t need electricity and parts hardly break down) and can perform calculations very rapidly.