A method includes inserting a vector in a packet that identifies a first device in a stack of packet forwarding devices to receive the packet. One end portions of the plurality of welding terminals are connected to one end portions of the electric wires of the harnesses, respectively, and the other end portions of the plurality of welding terminals are connected to the power terminals of the power circuit unit by welding, respectively. Loyalty units credits are calculated for a member from data obtained in the step of accepting. A light-source element emits light from a light-emitting surface and cooperates with a light-blocking sheet disposed between the light-source element and key rubber part and covers at least a portion of the light-emitting surface of the light-source element and has a loose hole through which the second protrusion of the key rubber part is passed. With this printing method, operations with respect to a printing apparatus can be performed with ease.