How is the book Yi Si Zhan written?

The part about astronomy in Yi Sizhan covers a wide range. When Li was young, he studied the works of Star Wars and made a lot of notes. During the reign of Yang Di the Great, many ancient books were lost, so he classified dozens of ancient books and compiled Yi Sizhan. Most of the articles about astrology come from ancient astrology books, but most of the contents about astronomy, calendars and instruments are his own research, which is very helpful to understand Li's scientific achievements.