Mr. Lai (1525-1604) in Ming Dynasty drew his version of Tai Chi diagram after studying 29-year I-Ching. There is a center circle inside the Yin Yang symbol. The center circle is called Tai Chi. According to I-Ching, Tai Chi is the original universe, then develops the Yin and Yang.
Tai Chi is one circle, then developed two elements - Yin and Yang. Next, it develops four phenomenon, eight trigrams (ba-Gua) ... and 64 hexagrams. This is binary system like the computer. It can develop down to 128,256,512... objects. However, that will be too complicate for human's mind. 64 hexagrams becomes the foundation of prediction. Any event can be developed 64 possibilities.