A card combination which is issued to a single cardholder can be reprogrammed by the cardholder for use by a sub-user to a desired extent with regard to value and time. The cardholder uses a master enabling code to access the programming mechanism. He/she assigns a sub-PIN for use by the sub-user and opens a subordinate account for the allowed credit value within card's total credit value. This subordinate account can be accessed using the sub-PIN. A limited term can be selected during which any transaction using the sub-PIN and using the subordinate account can be conducted. After the expiration of that term the sub-PIN is automatically erased and any balance in the suborinate account is re-credited to the main credit account of the card. Such a multi-user card can also be used in conjunction with a program for varying the value of units stored in the credit account.