What do the 72 lines refer to?

According to Qingbo Miscellany, the main industries in China's Tang Dynasty were "36 lines", namely: meat shops, palace powder, ready-made clothes, jade, jewelry, silk, paper, seafood, fresh fish, stationery, tea, bamboo, rice, iron, embroidery, needle and thread, and soup shops.

Xu ke said in the book "clearing banknotes, agriculture and business": "Thirty-six walkers, all kinds of occupations. As far as the division of labor is concerned, it is 36 lines, 72 lines for times and 36 lines for ten. " It can be seen that "seventy-two lines" is a virtual index, and the seventy-two lines or three hundred and sixty lines that people often say today are not specific figures. In fact, the division of labor in social industries has gone far beyond 72 lines.

Introduction to Thirty-six Lines:

Thirty-six Lines is a general term for all walks of life in the old days. Thirty-six lines are the general names of the major social industries in China in the Tang Dynasty, reflecting the division of labor of social industries at that time. Thirty-six lines extend the industry classification theory of seventy-two lines or three hundred and sixty lines commonly used in China. The exposition of thirty-six lines can be found in Zhou Hui's Qing Bo Zalu in Song Dynasty. Xu Ke said in "Clearing Banknotes, Farming and Business": "Thirty-six walkers, all kinds of occupations. According to the division of labor, it is 36 lines, 72 lines for times and 36 lines for ten times. " It can be seen that the 36 lines are only imaginary indexes, but they are not specific figures.