Originally a bookbinding term. In order to produce a complete book, the various parts must be collated in the right order. This is ensured by placing collation marks as check marks (in the case of books, usually at the spine of the book block) in a staggered arrangement from top to bottom. In passports, this type of register mark or position mark is an additional safeguard. It makes it easier to spot whether any pages have been exchanged or removed. It can be invisible under normal light, as a fluorescent overprint, or a visible feature (using normal or fluorescent ink). The combination of collation mark and page numbers is sometimes called floating numeration.