Abacus is known as “counting rod” which is calculating tool that was used for addition, subtraction, multiplication and division also people use for weight, amount, space, and volume of an object. It was invented about 1387 AD. The rules for abacus is simple once you know what todo and it is widely used in China. Also later on it was introduced to Japan and Korea and those countries still used now.
There is the basic first step of how to count the Abacus