It first appeared during China's Shang dynasty approximately 3,000 years ago and has since been adopted by other East Asian cultures such as Japan (shaku), Korea (ja/cheok), and Vietnam (thước).
In its ancient and modern forms, the chi is divided into 10 smaller units known as cun (the "Chinese inch").
[citation needed] The study of ancient rulers and other artefacts whose size in the contemporary chi was known allowed modern researchers to surmise that during the 2nd century BC to 3rd century AD the (Qin dynasty to Han dynasty to the Three Kingdoms period), the value of the chi varied between 23.1 and 24.3 cm (9.1 and 9.6 in).
[4] It is thought that the ancient Chinese astronomers also used chi as an angular unit; modern analysis of historical records indicates that it may have been equal to one degree.
In Guangzhou, however, the chi used for local trade varied from 14.625 to 14.81 inches (37.15 to 37.62 cm) – i.e., very close to the modern chek.