The beads on the abacus are divided into upper and lower layers by the middle beam, one is the upper layer and the other is the lower layer; The operation follows the decimal principle, and the multiplication is changed into addition and division is changed into subtraction by using the abacus formula of addition and subtraction. Through this transformation, four operations of addition, subtraction, multiplication and division are completed. 1, abacus is a tool for calculating numbers. The existing abacus has different shapes and materials. Generally, abacus is made of wood (or plastic). The abacus consists of a string of abacus beads with equal number arranged in a rectangular wooden frame, and a beam in the middle divides the abacus into upper and lower parts. Abacus beads run through a straight column, commonly known as "gears", and are generally in the 9th gear, 1 1 or 13 gear. There is a beam in the middle of the file, and there are 1 beads on the beam, and this bead is 5; 5 beads under the beam, each bead 1. 2. The abacus is rectangular, with a wooden frame around it and a small stick fixed in it. The wooden stick passes through the wooden bead, and the middle beam and abacus are divided into two parts. There are two beads in the upper part of each stick, five for each bead, and five for the lower part, one for each bead. 3. Abacus is called abacus, and abacus has corresponding rules corresponding to four operations, collectively referred to as abacus rules. With the use of abacus, people have summed up many formulas to make the calculation faster. Compared with general operation, skilled abacus calculation is not inferior to calculator, especially addition and subtraction. When in use, you can dial the abacus up and down according to the formula to calculate.