A credit card interest rate exchange and reduction method to benefit consumers who hold relatively high interest credit card debt and banks looking to invest non-income producing idle or excess cash on hand in the consumer marketplace. A saline water cartridge module includes a plurality of saline water cartridges arranged in a line, and feeding one saline water cartridge at each time under the control of a saline water cartridge feeding mechanism. A marker is placed a known distance from the rear of the vehicle. A unit number is derived from the east-west number and south-north number.