This video is called Rare medieval bookmark.
About this video, from Leiden university in the Netherlands:
Rare medieval bookmark found in Leiden University Library
A rare medieval bookmark emerged in Leiden University Library. Book historian Erik Kwakkel found the disk in an archive of manuscript descriptions called the Bibliotheca Neerlandica Manuscripta. It was likely put their [sic; there] in the early twentieth century by Willem de Vreese, who made the descriptions. The presence of the bookmark was not known to the library. Only thirty-five bookmarks of this type have been identified worldwide.
The bookmark concerns a disk with the numbers 1-4 written on it. Originally, it would have been fitted in a sleeve, which could be pulled up and down along a cord. The reader would turn the disk to indicate in what text column certain information was found, after which he pulled the sleeve to the relevant line. Page, column and line were thus marked. The specimen in Leiden is incomplete, as only the disk itself survived. However, this manuscript in Harvard’s Houghton Library illustrates how the bookmark works.
Although it is hard to determine the precise date of the bookmark, it was likely made in the thirteenth or fourteenth century. It appears to have been popular in learned books and it reflects how scholars from the thirteenth century began to use their books. No longer were the objects merely used to read from cover to cover, but an interest emerged to read particular sections. To facilitate such use, various aids became widely used, including the index, running titles, and detailed chapter titles. The rotating bookmark can be understood as yet another means to quickly and efficiently find your way to a particular passage. The thumbprints on the Leiden specimen suggests it was frequently used.
The bookmark has been moved to the manuscript collection and has been given the shelfmark BPL 3327. The find was first reported on Erik Kwakkel’s blog medievalbooks.nl and in De Volkskrant of 2 October, 2014.
Last Modified: 02-10-2014.