Numbers have the advantage of extending on into infinity. Letters as signatures must be repeated with distinguishing variations if the book is of some length. Many further variations of signatures are known to be possible, and others await discovery. Their detection offers the scholar, or even the casual reader, one of the few excuses for extended idle browsing in old books. Particularly noticeable are variations in the signatures of preliminary pages.
Authors tend to write their prefaces last of all, often when the book is already on press.
But elsewhere in the preliminary leaves it is sometimes possible to find an interesting assortment of unusual types, the asterisk, obelus, Maltese cross, paragraph, and various other marks of punctuation. It was more common, however, either to begin setting the type by signing the first page of the main text with the letter B, reserving for A the eventual preliminaries, or to begin the text with a capital A, reserving lower case for the preliminaries - or some combination of the two. Shakespeare's Poems, for instance, is octavo in format. That is to say that the large sheets of paper on which it is printed were folded three times to form four leaves, or eight pages. The way a book is put together, or assembled from the sheets, is called collation.