Abacus

　　The abacus is one of the most important counting instruments in ancient China and was called by some western writers as "the earliest calculating machine in the world".

　　The abacus was invented during the late Song Dynasty (960-1279) and the early Yuan Dynasty (1280-1368).

　　Lu Ban Mu Jing gave the most detailed description of the making and specifics of the abacus. The abacus drawn in the Shuxue Tonggui by Ke Shangqian in the 16th century was the same as current abacus. During the Ming Dynasty (1368-1644), abaci became popular and spread to East Asian countries.

　　Often referred to as the first computer, the abacus is used to add, subtract, multiply and divide, as well as figuring fractions and square roots. In certain Asian communities, abaci are still being used to calculate invoices. In the modern home, it makes an extraordinary desktop accessory.

　　A standard Chinese abacus consists of a frame divided by a middle bar into an upper and lower deck, with eight parallel rods running from top to bottom. Each rod has five beads on the lower deck and two beads on the upper deck. For calculations, each bead on a given wire on the lower deck has the same value: either ten or some multiple or submultiple of ten. The beads on the upper deck have a value of five each.

　　Calculations on a Chinese abacus are performed by placing the abacus flat on a table or one's flap and manipulating the beads with the fingers of one hand. People need nimble fingers to do it fast. Beads in the lower deck are moved up with the thumb and down with the index finger, with the middle or index finger used on the upper deck. Beads are counted by moving them towards the middle bar. The right-most rod is usually the ones column; to the left is the tens column next to which is the hundreds rod, and so on. After five beads are counted in the lower deck, the result is carried to the upper deck; after both beads in the upper deck are counted, the result (10) is then carried to the left-most adjacent rod. Decimals can be counted by choosing a space between two rows to designate the decimal point. All the rods to the right of that space then represent fractional portions.