A section of an old Hong Kong ruler, showing the last (10th) cun of a chi. One can see that the chi in that jurisdiction was exactly equal to 14+5/8 of an inch. A metric ruler is shown next to it for comparison.
A cun (Chinese: 寸ts'wun; Pinyin cùn IPA |mi=[tsʰwə̂n]), often glossed as the Chinese inch, is a traditional Chinese unit of length. Its traditional measure is the width of a person's thumb at the knuckle, whereas the width of the two forefingers denotes 1.5 cun and the width of four fingers (except the thumb) side-by-side is 3 cuns.[1] It continues to be used to chart acupuncture points on the human body, and, in various uses for traditional Chinese medicine.
The cun was part of a larger decimal system. A cun was made up of 10 fen, which depending on the period approximated lengths or widths of millet grains,[2] and represented one-tenth of a chi ("Chinese foot").[3] In time the lengths were standardized, although to different values in different jurisdictions. (See Chi (unit) for details.)
In Hong Kong, using the traditional standard, it measures ~3.715 cm (~1.463 in) and is written "tsun".[4] In the twentieth century in the Republic of China, the lengths were standardized to fit with the metric system, and in current usage in People's Republic of China and Taiwan[citation needed] it measures 3+1/3 cm (~1.312 in).
In Japan, the corresponding unit, sun (寸), was standardized at 1000⁄33 mm (3.03 cm, ~1.193 in, or ~0.09942 ft).
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