An energy-efficient consumer device audio power output stage with gain control provides improved battery life and reduced power dissipation without clipping the audio output signal. The layer-2 device receives a first test data unit from the source device, and defines a quality datum associated with processing the first test data unit. A piezoelectric resonator is mounted on the case substrate such that the piezoelectric resonator is bonded to the outer surfaces of the substrate electrodes by a conductive bonding material and is supported by the substrate electrodes in a point-contact manner. Arranging the heap further includes comparing first and second nodes to determine which has the sought benefit within the heap, and ordering the peak node as the head of the heap. Thus, both during holding and in applying to the vacuum heat insulator, the gas adsorbent can be applied to the vacuum heat insulator without degradation, and the high degree of vacuum can be kept for a long time. Provision is made here for a plurality of similar retaining devices to be arranged on the bearing device, wherein the pressure roller unit can optionally be secured to one of the retaining devices andor transferred between them.