What is Zhouyi about? Why is it related to the sum of fortune telling?

I have read Zhouyi, which has nothing to do with divination.

But generally divination is related to Zhouyi. Because the basic content of Zhouyi is quoted by divination, just like the calculation of physical chemistry quotes mathematics.

All cultures in ancient China were based on Zhouyi. From yin and yang, five elements, gossip, stem and branch, etc. , is the basis of ancient medicine, military, science and music (ancient five tones) in China. ...