An electronic device switches between an electronic book reading mode and an audio book playback mode in a manner that is convenient and intuitive to the user. In a digital processing system, an increase in current drawn by a peripheral device coupled to the digital processing system while the digital processing system is in a reduced power consumption state is sensed, wherein the increase in current drawn provides a current draw detect signal. The induced perturbations are manifest due to changes of resonance conditions and measured from changes in transfer characteristics or from changes of the scattering spectra of a microcavity-waveguide system. The first variable-process-parameter control loop has a gain. The cruciform parachute may be steerable andor may be configured to glide via inclusion of venting means on the parachute canopy. The vane is configured with respect to the housing such that a blower associated with the CPAP apparatus remains substantially unchoked, regardless of whether the vane is in the open or closed position.