The MECCA (Mechanized Catalog) system1 has been in use by Boeing Aerospace Group Technical Library since July 1, 1964. Designed to produce printed library catalogs and to generate a data bank for later machine retrieval, the system is a major modification of an earlier program.2 Prior to 1964, the library manually produced catalog cards for books and documents in its central library and four branches; this operation provided a complete catalog for the central location, while the branch library catalogs represented only the data held in each respective collection. A system was required that would produce complete catalogs for all library service areas and reduce operating costs as well. The library needed an output format that would conform to library standards and provide the following products: four sheaf listings (accession number, contract/document number, title/subject, and author lists) ; four duplicate sets of 3“×5” catalog cards for a twelve-month trial period; and a weekly announcement bulletin. Each input set for a single book or document would be identified by a variable number of descriptive elements such as author, title, contract number, subject, etc., which in turn would be manipulated into various arrangements according to the type of output list.