To be considered identical, watermarks must have the identical details or initials, countermarks, recognizable sewing dots, laid and chain line frequencies. The number of distinct watermarks is much greater than the body of published marks, and general types (i.e., fleurde-lis, IHS monogram) were in widespread use for a century or more. (Abstractor's note: Therefore, Nicholson's remarks on significant details to look for in a watermarked sheet and problems possible in interpreting information given for published watermarks are apt).