A group of seven (7) PINs are assigned to each card holder. The group of PINs are to be used in a specific sequence changing each calendar day. If a PIN is used out of sequence, then access to the charge or credit card is denied by the card company. A grid of numbers and letters are used to vary the...http://www.google.com/patents/US5251259?utm_source=gb-gplus-sharePatent US5251259 - Personal identification system
