Medieval manuscript lesson of the day: anti-theft edition! Here's an inventory of books from St Paul's Cathedral Library, written up in 1458. It is written in the form of n indenture, with wavy lines at the edge. Explanation in the next tweets. (BL Cotton Charter xiii.2) 
Two identical copies were drawn up then cut along this line, each held by a different individual (probably the two chaplains responsible for overseeing the library). At a given time, a chaplain would be asked to show this inventory next to its copy for a shelf audit.
This helped identify books missing from the shelves. The wavy lines ensure that the copies brought together were those written at the same time and are exact copies. This prevented the chaplain from forging a copy of the inventory which might leave off any books he had stolen.
