A discharge tube made of a dielectric material extends through a hole of a rectangular waveguide and through a coaxial microwave cavity so as to be coaxial with the central axis of the cavity. In a medium that recordsplays back data including video data and control information, the control information includes information for accessing a specific portion of the video data. The equivalence signature is computed as the functional for the kinetic energy of a point particle whose path is specified by the values of the digital data. The retainer frame is turnable away from and toward the horizontal bars for moving between an open position, in which the cook unit can be placed in the receiving space, and a closed position, in which the retainer frame engages releasably the first connecting rod for retaining the cook unit in the receiving space.