The center is explained by pen nouns.

"Center" refers to the position of the front end of the pen in the stroke line running, so that the pen holder is vertical, the pen tip runs in the middle of the stroke, and the lines are even, round and full, which has a three-dimensional sense, which is different from "oblique front".

"Centering" is usually called "positive front", and "centering" has been the "eternal difficulty" criterion in calligraphy pens since ancient times. Jiang Baishi's "Continued Book" said: "I always want to write in the painting, and both sides are sick." Shen Kuo in the Northern Song Dynasty also recorded in Meng Qian Bi Tan that Xu Xuan was good at seal script in the Song Dynasty and reflected it in the sun. There is a wisp of thick ink in the center of the painting, and as for the bend, it is one of them. It is because the pen tip can't fall straight down, so the pen tip is often in the painting, so this pen method is also used.

In order to clearly distinguish the concepts of "center" and "off-center", the attached drawings will be explained later: