WUC manuals are used to identify all "work unit" (support general and equipment identification), "type maintenance," "action taken," "when discovered," and "how malfunctioned" codes that apply to the equipment covered by the manual. Under the Air Force data collection system, each maintenance action performed on Air Force equipment must be fully and accurately documented. The volume of data collected requires the use of Automatic Data Processing (ADP) techniques. The use of ADP equipment requires that the data input be coded in such a manner that it can be read by the data processing machines. Standard codes have been developed for recording the type of maintenance being performed, the action taken to correct a deficiency, when a deficiency was discovered, and the type of malfunction that occurred. Identification codes, called "work unit codes," are used to identify the specific assembly or part within an end item on which an action was performed.