The center refers to the pen used in the center, which means that the pen tip always stays in the middle of the stroke trajectory and runs vertically downward. The lines written in the center are full and powerful, with a three-dimensional sense. The ancients said: "Make the pen heart always move in stippling", that is, the center refers to the pen.
The center pen can't be too dry, and it can't be finished at once. You should lick the pen at any time as needed and keep it "conical". Therefore, for the center, there are two kinds of calligraphy effects: one is "folding hairpin"; Second: "Leak marks". The lines of the two special effects give people a sense of beauty, but the charm is completely different, one is "charming" and the other is "vigorous". The former writes fast and the latter writes slowly. Of course, deliberately fast or slow in writing can't achieve the goal. This is also related to the skill of calligraphers.