A fluid dynamic bearing design featuring a shaft, a first and second conical bearing affixed, respectively, to a first and second end of the shaft, and asymmetric seals on each bearing. The latter stops the materials relative to the road and confines, or packs, them on the road. A distribution of the material within the region is estimated, responsively to the measured intensity of the X-ray fluorescence and to the intensity cross-section of the excitation beam, with a spatial resolution that is finer than the beam-width. The pre-conditioned polishing pad facilitates uniform polishing rates of production semiconductor wafers subsequently polished on the apparatus.