A power tool, such as a drilldriver or a reciprocating saw, can be provided with a belt clip which attaches to the tool at multiple positions to adapt to the user’s preference. The invention provides an imaging optical system comprising at least one decentered prism 10 having a rotationally asymmetric reflecting surface, at least located on an image side of an aperture stop. For the acoustic signature of the recorded chirp, the computer can characterize the acoustic environment in which the recording was made and use those characteristics to improve the remainder of the audio.