and put a magnet next to them. press down with your fingers and feel the height of the pages next to the magnet. add or remove pages from the pile until it's the exact same height as the magnet.
note: if you're having a hard time getting it exact, fall on the side of too few pages rather than too many. better for the magnet to be thicker than the pages, than the other way around.
punch three holes in the stack of pages.
using a single hole punch, put three holes on the side of the page, one each at the top, middle, and bottom. these holes are where the cover magnets 