What does the symbol "-"in the ancient "Eight Diagrams" in China stand for?

Bagua: A set of symbols in ancient China. With "one" for yang and "-"for yin, three such symbols form eight forms, which are called eight diagrams. Each six-pointed star represents something. Dry represents heaven, Kun represents earth, ridge represents water, far represents fire, earthquake represents thunder, root represents mountain, Xun represents wind, and dui represents swamp. Eight diagrams are matched with each other to get sixty-four hexagrams, which are used to symbolize various natural phenomena and personnel phenomena. It is discussed in detail in the Book of Changes. Gossip is said to have been created by Fuxi and later used for divination.