What's the secret of the secret?

Books on divination and astronomy. According to historical data and documents, the secret code was first formulated by Emperor Wu of the Han Dynasty at that time, and later spread to the Tang Dynasty and the Ming and Qing Dynasties. Among them, Sun Simiao, a Taoist priest in the Tang Dynasty, once wrote a book about the secret code, calling it the change of Yin and Yang, the love of the four seasons and five elements, and saved almost one book. In addition to the Secret Code, there are many classic works, such as The Book of Changes, Luo Shu, Zhouyi Yi Tong, etc., which have had a far-reaching impact on the development and theoretical construction of divination.