A book was tagged with a unique identifier (a shelfmark) that was entered into a searchable database (a library catalogue), which could subsequently be consulted with a handheld device (a portable version of the catalogue).
It comes in the form of a book with a peculiar shape… It is long and narrow, a format that indicates it was made for handheld use… What a clever tool the user ended up with. The open catalogue in his hand presented two columns, one for books on the "black" (left-hand side) side of the lectern, another for books on the "red" (right-hand) side. Moreover, each column is divided into two halves. The top half lists books placed on the upper shelf of the lectern, the lower half those on the lower shelf.Standing in front of a lectern with his handheld device, the reader knew precisely which of the volumes in front of him was the one he was looking for: he could identify it without even opening it. This particular medieval catalogue is not unlike a modern navigation system, with "GPS coordinates" directing readers to such works as Ambrose on the Psalms (Black A 1) and Augustine's Civitate Dei (Red A 5).The only difference is that it never ran out of batteries.