Central calligraphy terminology. When stippling with a pen, keep the main front of the brush on the center line of stippling to distinguish it from the partial front. The money note written in the center is round and textured. In Meng Qian Bi Tan written by Shen Kuo in the Northern Song Dynasty, it was recorded that Xu Xuan was good at seal script in the Song Dynasty, and it was reflected in the Japanese. 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.