We have discovered a method of reducing the effect of material sputteredetched during the preheating of a substrate. The trays are arranged into a stack, such that their respective side hinging surfaces line up with each other to form a composite hinging surface. Moreover, sufficient substrate material is removed from the substrate to sufficiently lessen stiffness of selected ones of the contact portions so that the selected ones of the contact portions are independently displaceable with respect to each other. In use, a compressed gas is supplied to theeach chamber from the reservoir, the buoyancy of the gas applying an upward force to a portion of the chamber, the upward force moving at least a portion of the chamber from a first position to a second position, the movement of the at least a portion of the chamber adapted to drive the output device to provide a continuous apparatus output. An Independent claim is also included for an arrangement for implementing the method. The single loop headstrap extends from the mask at either end.