A white balance control amount calculating device, provided in an electronic still camera, comprises an imaging device by which an image signal of a subject is sensed. The system detects if there is a substantial difference between, on the one hand, a power drawn from the primary unit and, on the other hand, a power required by the secondary device or, if there is more than one secondary device, a combined power required by the secondary devices. The average release time from the traps may be longer than the period of any present RF signals, thereby effectively immobilizing the surface conduction layer, which may substantially prevent capacitance and inductance changes due to the RF signals. The securing assembly has an anchor member that in a secured configuration maintains the rack frame in abutment with the pickup truck bed so that the rack frame is substantially fixing relative to the truck bed.