accounting records, validation procedures are most effective when they are performed as close to the source of the transaction as possible. In the batch purchases system depicted in Figure 10.1, validation of purchase orders occurs only after they have been sent to the vendor. Because of inevitable transcription errors that occur in preparation of source documents, such systems are characterized by the need for extensive error correction and transaction resubmission procedures. On the other hand, the real-time input of timecard data illustrated in Figure 10.6 can identify and resolve most errors as they occur. This approach also minimizes human data entry and thus reduces the risk of data entry errors. For example, when the clerk enters the employee number, the system automatically retrieves his or her name, mailing address, pay rate, and other relevant data from the employee file.