There is a circle in the middle of Tian Zige, which is a form of calligraphy practice to practice writing Chinese characters. On the basis of Tian Zige, this format divides the middle cross into four parts, and each part has a dot to form eight squares, so it is called eight squares. The point of octagonal lattice is located in the center of Tianzi lattice, which plays a role of balance and symmetry.