Abstract: A system used to provide a verification check of a credit card or credit document includes a large capacity read/write memory having a single binary data bit stored at each address location. The credit card has unique identifying information encoded on it for addressing a specific location in the memory. A readout is provided in response to the insertion of the credit card to indicate whether the card is a valid one or not. To program the memory initially, a provision is made for individually addressing each of the different memory locations and to establish a "valid" or "non-valid" binary data bit storage at each location corresponding to a different credit card. In addition, manually operable addressing switches are provided to change the specific bit stored at any given address subsequent to the initial storage of data in the memory.