(from the encyclopedia, with a more detailed explanation)
Historical allusion
Before the Qin Dynasty in China, coins and units of measurement in various countries were not unified, and transactions between businessmen and people in various countries were not convenient. After the Qin Dynasty unified the six countries, Qin Shihuang ordered a unified survey, and Li Si was responsible for drafting documents. At that time, the standard of measurement had been basically determined, but this "scale" was still undecided, so I went to consult the first emperor. Qin Shihuang then began to write down the four characters "justice in the world".
Reese took four big characters and was puzzled. In order not to let the emperor blame him, he simply added the four-character strokes together and became a unit of "balance". One catty equals sixteen taels, so half a catty is eight taels, which is exactly the same.
It was used in China feudal society for more than 2000 years. It was not until after the founding of New China that it was changed to the present situation that one catty is equal to twelve due to the inconvenient calculation of the sixteen-two-system system.