System for keeping account of predetermined homogeneous units

A credit card for keeping a record of predetermined homogeneous credit units, said credit card being adapted to be used with external means for imprinting and/or operating on information stored on the credit card, the credit card comprising:

• a memory circuit for storing coded information, said memory including:
• (a) a first unalterable multi-bit field indicative of an identification of the external means with which the card can be used,
• (b) a second unalterable multi-bit field indicative of operations that can be performed with the card on the external means with which the card can be used, and
• (c) an alterable multi-bit field indicative of the number of credit units available to the holder of the card;
• circuits for reading bits from the alterable multi-bit field and from the first and second unalterable multi-bit fields and for writing bits into the alterable multi-bit field;
• and
• means for temporarily and selectively coupling the memory and circuits to the imprinting and operating means, each of the first and second unalterable bit fields including n bits, a change from one bit state to the other bit state of bits in the unalterable fields being in an irreversible state after imprinting of bits therein, the number, m, of bits in the irreversible state in each field being less than n, the number m being pre-established.