A method of marketing goods andor services using discount purchasing incentives. The body has a stop in each end and two compression springs within the tubular body between the stops. An adjustment hole is configured on the grip cover mount part to releasably engage the grip cover with the hook and adjust a travel system adjustment member. The stopper can allow the locking surface of the stopper engagement section to freely rotate when the first hinge section rotates by a predetermined angle. The receiver is adapted to receive the transmitted signals and to recognize whether the barrier signal or the passageway signal is being generated and transmitted. A magnetic under layer of a two-layered perpendicular magnetic recording medium includes three layers: a ferromagnetic layer; a non-magnetic layer; and a ferromagnetic layer, wherein the ferromagnetic layers are antiferromagnetically coupled with each other, thereby preventing a magnetic flux from a magnetic wall in a magnetic under layer from entering a read back head.