Although not the first to invent pop-up books, he was the first to invent automatic pop-up books. Before Nister, pop-ups had to be manually maneuvered into an upright position."Pop-up books" is a term sometimes applied to other movable books, volvelles, tunnel books, pull tabs, and other varied forms of paper engineering; similar techniques such as die cutting and embossing are often also used in greeting cards. Children's books with movable parts are subject to the play of children and may not work properly after heavy use. Older mechanical books in library or personal collections can be preserved by professional conservators. The older original first edition books by Ernest Nister can be found in antiquarian book stores and the archives of Library rare book collections.