Some library costs and options

The annual costs associated with investment in bookstock and storage capacity, and with operating them, are weighed against the extra operating costs that would be incurred through reliance on inter-library loans instead of one's own stock. On these cost grounds, it seems to be worth acquiring, and providing storage for, books likely to be wanted more often than once in about 1·7 years over a long period. It also seems that it is cheaper to discard books already in stock, rather than building additional storage space of reader-access quality, if the books in question have a prospective frequency of use that has fallen below once in about 13 years. Storage space of quality lower than that required for reader-access can be provided at about half the cost per book estimated for reader-access storage, but it seems likely that for infre quently-used material (e.g. less than once in 20 years ), inter-library borrowing will be cheaper than even cheap storage. All these estimates, however, disregard in-library use of books, and the cost to readers of delays associated with inter-library borrowing; they are thus biased in favour of such borrowing to an unknown extent.