Counting rods

Counting rods (traditional Chinese: 籌; simplified Chinese: 筹; pinyin: chóu; Japanese: 算木; rōmaji: sangi) are small bars, typically 3–14 cm long, that were used by mathematicians for calculation in ancient China, Japan, Korea, and Vietnam. They are placed either horizontally or vertically to represent any integer or rational number.

The written forms based on them are called rod numerals. They are a true positional numeral system with digits for 1–9 and a blank for 0, from the Warring states period (circa 475 BCE) to the 16th century.

Counting rods were used by ancient Chinese for more than two thousand years. In 1954, forty-odd counting rods of the Warring States period were found in Zuǒjiāgōngshān (左家公山) Chu Grave No.15 in Changsha, Hunan.

In 1973, archeologists unearthed a number of wood scripts from a Han dynasty tomb in Hubei. On one of the wooden scripts was written: “当利二月定算”. This is one of the earliest examples of using counting rod numerals in writing.

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