First, put a book like this and open the first page of a book then, write "1" down on the page. The page will be the first page to fold.
Write 10, 20, 30, down every 10 pages until reaching last page of the book.
Make a line at 50mm from top of the book. The point will be top of your pattern. We call the point 0mm point.
The red line required all the pages so we draw a line with a post it.
Put a post-it on the first page to fold and last page.
Make a vivid line along with right side of the post-it, after that take it off.