Why is Kaiyuan Zhan Jing a classic of astrology?

This book comprehensively compiles the achievements of China's ancient theory of the universe, a large number of records and divination judgments about celestial bodies, astronomical phenomena and meteorological changes, as well as the basic data of 29 calendars such as Indian Nine Calendars and Linde Calendars in the early Tang Dynasty and other astrological documents. This is a veritable astrological classic.