Suan Chou

　　Counting rods (chou) were the first tool the Chinese used to calculate. Calculating with the rods was a system known as Suan Chou.

　　The rods were made mainly of bamboo, though some were made of bone, wood and other materials. They were the precursor to the abacus. Counting rods were regarded as being approximately six Chinese inches long and one tenth of an inch in diameter. (A Chinese inch ranged from 22.5mm to 33.3mm)

　　In Suan Chou, counting rods can be represented either horizontally or vertically. This was done in order to make it easier to determine which place value a certain number is in. Units are represented vertically, the tens place is represented horizontally, the hundreds place vertically, the thousands place horizontally... This pattern of alternation continues to whatever place is needed. Unlike written texts that are read from top to bottom in China, all numbers are read from left to right.

　　There is no clearly defined time of when counting rods were brought into Chinese mathematics, but evidence seems to point to the first half of the Warring States Period (481-221BC). Suan Chou was the most important counting tool before the birth of the abacus.