The essence of theft prevention is stock control and vigilance. If a library is uncertain about the types and quantities of materials it has in its possession, determining whether and when a theft has been committed will be almost impossible. If library materials are not clearly identified and described, proof of ownership will be difficult to establish even if stolen materials are discovered in someone's possession.
In collections of moderate size, inventories can help determine the state of completeness of the stock. If the collection is too large for a full inventory, parts of the collection can be inventoried on a rotating schedule, with special collections of rare and unique materials being checked on a regular basis.

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