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THE SIZE AND PROPORTIONS OF A BOOK depend on the size of the original sheet of paper used to produce the book. For example, if a sheet measuring 480 × 640 mm (19 × 25 in) is used to print a quarto, the resulting book will be approximately 320 (h) × 240 (w) mm (12 ½ × 9 ½ in) before trimming. The exact size of paper used has differed over the years and localities, meaning sizes of books produced in the same format can differ. For example, a 16th century French or Italian octavo is approximately the same size as a modern mass market paperback book, but an 18th century English octavo is noticeably larger — more like a modern trade paperback or hardcover novel.