"The IBM 6400 can handle complicated accounting procedures like billing, inventory, and accounts receivable in a single machine operation. The key to this new simplicity is the IBM 6400 Magnetic Ledger Card. Information important to you is posted on the face of the ledger card. Information important to the IBM 6400 is recorded on a strip of magnetic tape on back of the card. The IBM 6400 reads and cheks all data on the magnetic strip."