The Library of Congress uses letters to designate large disciplinary groupings and numbers to indicate subordinate parts of these classes. For instance, R represents Medicine and RD118 represents Plastic Surgery.
Library of Congress call numbers involve alphabetic, numeric, and character-by-character sequences and are used with materials in most of the UNB WorldCat locations. The main exceptions are the locations described in conjunction with Dewey Decimal call numbers and Government Documents call numbers.
Here is an example of a Library of Congress call number as it appears in a UNB WorldCat record:
F1629 .E17 A37 1996
On the book spine this call number appears as:
F
1629
.E17
A37
1996
Decoding this sequence is a matter of using appropriate rules for each line. The first line is alphabetic and may consist of one, two, or occasionally three letters. The next line is numeric and is always less than 9999. It may or may not have a decimal portion, but the shelf sequence treats this line as a unit. 1629 precedes 1629.3, which precedes 1630. The third line and any subsequent lines, consisting of alphabetic and numeric characters, file in character by character fashion. E165 precedes E17, which precedes E2. The last line is a dateline and sequences materials numerically.