In book publishing, casting off is the process of estimating the number of signatures required to typeset a manuscript. An accurate castoff (or cast off) is important because the page length of a book affects many variables, including the cost of producing the book, the cover price, how many books can fit in a carton, and the width of the spine. While some software exists to help editors in accurately casting off manuscripts, even an experienced editor often can't foresee the many variables that will affect a book's length, some of which may not arise until the book is well into production.