Seosan, also called seosu, is a tool used for counting and marking the number of times for which a book has been read. In the past when there were not many books to read, a book was often read several times and occasionally memorized for exams. Seosan was made by pasting several pieces of paper in a layer in the shape of an envelope, which was then stiffened. On the surface, ten or more slits were made to mark the number of times the book has been read by folding the slits backwards. The folded part was generally made noticeable by painting the outer surface in black and the inner part in white or red. The top, bottom, or middle part of seosan was cut out in the motif of a chrysanthemum, a bat, or a butterfly to vary the otherwise monotonous design. The seosan shown here was painted with ink on its exterior. There were joins along the edge, which were folded inwards like an envelope, to prevent the paper-made body form being torn easily. It has three slits at the upper part, ten slits at the lower part, and a bat design cut out in between.