In "Huai Su Calligraphy", there is such a description: "The lack of books is to draw a plate of books and a board, and the books are repeatedly ground." This description is about Huai Su's writing.
Specifically, this description can be understood as follows: Huai Su didn't have enough books at hand, so he drew a plate as the basis for copying characters, and then drew a square board as a tool for describing glyphs. He practiced writing repeatedly, writing more and more times, and the paint on the board and board was worn out.
This description shows Huai Su's spirit of assiduous study of calligraphy. He is not only satisfied with the existing paper, but tries to use things around him to practice and improve his calligraphy skills. This persistence and hard work made Huai a great artist in the history of calligraphy in China.