When marking a manuscript or block copy, there are two sides when marking the page number, and ab should be used to mark or distinguish up and down when marking. Click to open a copy of the school-based collation, and the page number is usually the currently printed page number, which is expressed in Arabic numerals.
The ancient books in our country are all arranged vertically, looking from right to left. After turning the page, if the right side is 2, the left side is 3. And so on.