For example, a modern novel may consist of gatherings of sixteen leaves, but may actually have been printed with sixty-four pages on each side of a very large sheet of paper.[6]: 429 Similarly, the actual printing format cannot be determined for books that are perfect bound, where every leaf in the book is completely cut out (i.e., not conjugate to another leaf as in gatherings) and is glued into the spine. Modern books are commonly called folio, quarto and octavo based simply on their size rather than the format in which they were actually produced, if that can even be determined. Scholarly bibliographers may describe such books based on the number of leaves in each gathering (eight leaves per gathering forming an octavo), even where the actual number of pages printed on the original sheet is unknown[4]: 80–81 or may reject the use of these terms for modern books entirely.[note 1]