Credo Reference This link opens in a new windowThe Credo Reference database is a digital collection of encyclopedias, dictionaries, and almanacs, and can be a great place to start to learn more about the history of a time period or of a specific type of media. Tertiary sources like encyclopedias are particularly useful in gathering keywords on media formats that can be used to search primary resources and archives. For example, an encyclopedia entry on "typewriters" can reveal different brands to search (e.g., Remington, Blickensderfer, International Business Machines), time periods (1860s — 1980s), and people (e.g., Mary Foot Seymour, who opened the first typing school in New York City).