Data, for example, data relating to a bank account, is carried on the person in the form of a small portable means such as a flat card containing encapsulated logic microstructures. The circuitry includes a memory and its control circuits, with inhibitor means preventing access to predetermined sections of the memory. The portable means cooperates with data-transfer means provided at fixed locations. Credit entries in the card are summed and the debit entries are summed and subtracted from the credit entries. Any credit balance may be used to effect a purchase or to obtain an issue of cash money. Coupling of the card and data-transfer means is effected optically by light-emitting diodes cooperating with photovoltaic piles, or by direct electrical contact. Prohibited memory sections carry a code actuating a lock-out latch system. Alternatively a predetermined collection of addresses in the memory is prohibited, setting up one of these addresses actuates the lock-out.