When a horizontal line in a word is longer than the general horizontal line and plays a role in stabilizing the center of gravity, it becomes the main pen of the word. For example, the top horizontal of the word "Xia", the middle horizontal of the word "Ten" and the bottom horizontal of the word "Straight" are the main strokes. The ancients used horizontal paintings above, middle and below as the main strokes, which were called "Tian Gai", "Zhong Yao" and "Di Zai" respectively. Its function, like a tightrope acrobat holding a balance bar, is much smoother than unarmed.
"Vertical drawing of three-dimensional figures". A word may have more than one main pen, and vertical painting can also be the main pen. For example, the words "down, ten, straight", in addition to horizontal painting is the main pen, vertical painting is also the main pen, playing an auxiliary role.