Apparatuses and methods for monitoring microfeature workpiece rotation during processing, such as brushing, by monitoring characteristics corresponding to a state of a magnetic field proximate to the rotating microfeature workpiece are disclosed herein. A piston moving in an inner chamber compresses gas in the chamber. The first component defines a channel extending between the two opposing ends. The support part has a cover plate, which covers the intermediate space in one transverse direction. Preferably, integrating measurements of a plurality of internal supply voltages are performed in parallel during the same measurement time interval.