The Central Decimal Correspondence Files basically consist of correspondence that went through the Central Filing system, and includes carbons, original letters, telegrams, memorandums, transmittals, and notes. In many instances, the files contain attachments, such as photographs, blueprints, line and three-view drawings, forms, news clippings, transcripts of proceedings, brochures, publications, and various kinds of reports.  In some cases, these reports are the same type as can be found in the R & D Case Files, including detailed specifications, performance tests, structural analyses, and the like.