When you're using a reference book or other resource in the library that can't be checked out, do yourself a favor and jot down the name of the book and its author before you leave for the day.
Why?
Besides needing citation information for a formal report, you might need to come back and use that book again before your research is over. It's a lot easier for the librarian to help you find the book again if you remember more about it than how big it was or its color. Librarians are smart, but you give them quite a challenge if you ask them to find that "very large green book" that you were using last Thursday.