by the image above, was used to simplify and speed up addition and subtraction somewhat, as well as to decrease the chances of error. Its use was demonstrated, for example, in the first book devoted entirely to suanpan: Computational Methods with the Beads in a Tray (Pánzhū Suànfǎ 盤珠算法) by Xú Xīnlǔ 徐心魯 (1573, Late Ming Dynasty). The following two animations show the details of this particular usage: The beads and rods are often lubricated to ensure quick, smooth motion. Calculating on a suanpan At the end of a decimal calculation on a suanpan, it is never the case that all five beads in the lower deck are moved up; in this case, the five beads are pushed back down and one carry bead in the top deck takes their place. Similarly, if two beads in the top deck are pushed down, they are pushed back up, and one carry bead in the lower deck of the next column to the left is moved up. The result of the computation is read off from the beads clustered near the separator beam between the upper and lower deck. Division There exist different methods to perform division on the suanpan. Some of them require the use of the so-called "Chinese division table". The two most extreme beads, the bottommost earth bead and the topmost heaven bead, are usually not used in addition and subtraction. They are essential (compulsory) in some of the multiplication methods (two of three methods require them) and division method (special division table, Qiuchu 九歸, one amongst three methods). When the intermediate result (in multiplication and division) is larger than 15 (fifteen), the second (extra) upper bead is moved halfway to represent ten (xuanchu, suspended). Thus the same rod can represent up to 20 (compulsory as intermediate steps in traditional suanpan multiplication and division). The mnemonics/readings of the Chinese division method [Qiuchu] has its origin in the use of bamboo sticks [Chousuan], which is one of the reasons that many believe the evolution of suanpan is independent of the Roman abacus. This Chinese division method (i.e. with division table) was not in use when the Japanese changed their abacus to one upper bead and four lower beads in about the 1920s. Decimal system This device works as a bi-quinary based number system in which carries and shifting are similar to the decimal number system. Since each rod represents a