The second aspect of maintenance work is book conservation. Only books in good physical condition should be allowed to stay on shelves. Constant shelf checking would remove torn, soiled and damaged books from shelves for repair, rebinding or to be withdrawn from circulation. This is a healthy practice and should never be underestimated. Another important aspect of conservation is that the stacks must be cleaned regularly to protect books from dust, dirt and insects. Airconditioning of stack rooms would be ideal to protect books from dust, heat and moisture. All these efforts are to aid the fundamental task of locating a book when it is wanted and returning to its assigned place when it is no longer needed; maintaining the order of books and taking care of the books that they are wanted again: All these tasks are usually entrusted to a maintenance section/division in addition to the other functions.