Method of storing a consumed amount in a card memory

Claim 1

A data recording method in a card memory in which a consumed amount up to a predetermined natural number P is recorded, which comprises the steps of: setting a predetermined natural number N so that said value P is exactly divisible by N and obtaining a quotient Q through a division of P/N; providing a first recording area on said card memory having an adequate number of record bits (a through j) equal to the obtained quotient Q which are unchangeable when marked so as to provide high security; providing a second recording area on said card memory having changeable memory means (M) and recording an initial value in said second recording area; dividing said consumed amount by said natural number N so as to obtain a quotient q and a remainder; recording said quotient q in said first recording area unchangeable by marking up to the same number of record bits as said quotient q; reproducing a value recorded in said second recording area; adding said remainder to said reproduced value so as to obtain a sum S; and recording said sum S in said second recording area as a new value when S is less than N, and when S is at least as great as N, recording the difference S-N in said second recording area as a new value and marking one more record bit in said first recording area.