That is, wooden slips, also known as wooden books, printed books or printed slips, are a form of books made of wooden boards with certain specifications (a few with triangular wooden columns) after writing words. According to records, there are several specifications of wooden slips, but the most common one is 1 square foot, and the thickness is 1 inch, that is, "one foot and one inch", which is commonly known as "ruler slips". Mostly used in calligraphy and painting.
Footprint was originally the name of a style. Bamboo slips refer to the wooden slips used by the ancients when writing. They use wooden slips with a length of one foot as letters, so they are called ruler books. Later, it became synonymous with letters. Due to the prosperity of personal correspondence, it provides a broad space and stage for the development of calligraphy. From the perspective of calligraphy, letters and correspondence have gradually become a special form, and have evolved into forms of expression such as book (poem) drafts, memorials, plaques, couplets, banners and fights.
But the word "ruler" has no specific meaning and is not commonly used. For example, giving a ruler means copying a work, and the meaning can be imagined. There is no such word in fixed words.