For performing basic addition, subtraction, multiplication and division, the suan pan, or 'calculating plate,' has been in use since the 15th century. Each of the two bead registers represents a unit of five; each of the five bead registers represents a unit of one. For further discussion of the history and use of the Chinese abacus, see Y. Yamazaki, "The Origin of the Chinese Abacus", Research Department Memoirs, Tokyo, 1959, no. 18, pp. 91-140.