Search the Olin Library catalog
Specific call numbers for books are found in the online catalog, but when browsing the shelves, it helps to know something about them.
Books about the Vietnam Conflict can be found shelved in the library in the call number range DS557 through DS559.9; the history of the country Vietnam starts in DS 556. However, American history from the Kennedy through the Ford administrations can be found from E 841 through E 865, and where the Vietnam conflict overlaps with other times books might be classified with other materials on that topic; for example, Songs of the Vietnam Conflict can be found under ML3477 .P45 2001 Works that address Vietnam
The broad topics indicated by the first letter of the "call number" are often broken down into subtopics with a second letter, and are then refined in much greater detail with the addition of numbers. A full listing of Library of Congress call numbers can be found here: http://www.loc.gov/catdir/cpso/lcco/
The digits in these call numbers are read as counting numbers, not as decimals as in the Dewey Decimal system. This means that DL 1175 is found between DL 1174 and DL 1179, well after DL 117 or DL 118.
This arrangement of books by subject matter makes shelf-browsing convenient. If you find a useful book, the books nearby on the shelf are likely to be closely related in topic.
Note that these call numbers are used both for the circulating collection, of which numbers beginning with E and F are all on the third floor of Olin, and in the reference collection, which is primarily on the second floor.