A system and method to efficiently use a plurality of \u2018receivers\u2019 to monitor a larger plurality of \u2018sources\u2019 for audio content. Both EL elements and photoelectric conversion elements are arranged in each pixel of a display device in an information device of the present invention having a pen input function. The antenna element is coupled to the ground plane and resonates within at least one predetermined frequency band for transmitting and receiving the radio frequency signals modulated at one or more frequencies within the at least one predetermined first frequency band. This three dimensional load model is then used to design the truck body in an iterative process until the volume of the truck body and the distribution of weight of the three dimensional load model on the truck chassis is substantially the same as the desired volume and the distribution of weight on the truck chassis. An apparatus and interface for transaction toggling based on proximity limits are also provided.