学进去

People started using the abacus（算盘）over four thousand years ago to calculate numbers. It was used in ancient China, Rome, Egypt and Greece. 1． The Chinese abacus is called Suan Pan and is made of beads and thin rods. The beads and rods are usually kept in a wooden frame. A horizontal bar divides the abacus into upper and lower parts. The upper part has two beads on each rod and the lower parts have five beads on each rod. 2． Each bead above the bar represents five while each bead below the bar represents one. There are more than seven rods for a Chinese abacus. Starting from right to left, the first rod is one, the next rod is ten, the third rod is hundred, etc.

When using the Chinese abacus, the first thing to do is to clear the numbers. 3． When a bead above the bar is moved down, or when a bead below the bar is moved up, it becomes active and takes value. Recording numbers on an abacus is quite easy. To represent one, simply push up one bead on the first rod below the dividing bar. 4． It is quick and easy to add or subtract numbers with an abacus. 5． A really good abacus user can even calculate square roots.