Using the Library of Congress Subject Headings can help you to identify the proper terms to use for searching the Online Catalog and other Databases. For example, suppose you wanted to find sources on the history of England. If you look under England - History it says USE Great Britain - History. This then is the proper term to use when doing a subject search in the Online Catalog. Below is an example of an entry from the Library of Congress Subject Headings volumes including an explanation of the symbols.
| Agricultural machinery (May Subd Geog) |
| [S761-S760.5] |
| UF Agriculture-Equipment and supplies |
| Crops-Machinery |
| Farm machinery |
| BT Machinery |
| RT Farm Equipment |
| Farm mechanization |
| Machine-tractor stations |
| SA subdivision machinery under names of crops e.g. Corn-Machinery |
| NT Agricultural implements |
| Agricultural instruments. |
| EXPLANATION: |
| Agricultural Machinery - heading in boldface used for subject searching. |
| (May Subd Geog) - place names may follow the heading. |
| [S671-S760.5] - call number indicates where most books on subject are found. |
| UF - (Used For) - refers to headings which are not used in LC. |
| BT - (Broader Topic) - refers to more general headings. |
| RT - (Related Topic) - other terms related to heading in boldface. |
| SA- (See Also) - another way of looking up the same topic. |
| NT - (Narrower Topic) - more specific headings than boldface heading. |