A Medieval Revolving Bookmark, manuscript on vellum
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a rectangle of vellum folded to 41mm. by 22mm. and stitched loosely around a string so that it can slide up and down, partly sandwiching a circular disc of vellum also stitched so that it revolves with the emerging quarter showing numbers inscribed on one side of the disc in roman numerals ‘i’ to ‘iiii’ (touched in red) and on the other in arabic numerals ‘1’ to ‘4’, the outline of the disc and its quarters drawn also on each side of the rectangle; from the Rooryck Collection
The upper end of the string would be attached to a manuscript’s headband. It could be located between any two pages, and the marker could be slid up or down the string to the exact level to be marked, and the disc would then be turned to indicate column 1 or 2 on the left-hand of the opening or 3 or 4 on the right. About 30 such rotating bookmarks have been recorded in continental libraries (cf. J. Destrez, ‘L’outillage des copistes du XIIIe et du XIVe siècles’, Aus der Geisteswelt des Mittelalters, Martin Grabmann festschrift, 1935, pp.19-34) and about half a dozen from England (cf. R. Emms, ‘Medieval Rotating Column-Indicators’, Transactions of the Cambridge Bibliographical Society, XII, 2001, pp.179-84).