Alfred William Pollard,
1911 Encyclopædia Britannica, Volume 3…
(1911)
“ In a folio book one of every pair of leaves should have a watermark in the middle of the paper. In a quarto some pairs of leaves will have no watermark; in others it will be found divided by the fold of the paper. As the great majority of books without printed signatures are in folio or quarto, the sequence of watermarked and un-watermarked leaves, if carefully worked out, will mostly reveal the “make-up” of the successive gatherings. ”
