Machine-readable light-colored or invisible, but luminescent, postage-evidencing symbology and dark, readable other postage information are printed, preferably in a single print operation, to provide large amounts of information without diminishing read rates. The rotor is provided with permanent magnets and has a pole pair number of 2p with a pole pitch width p, wherein the pitch ratio spp is 2. A blade of a skate is inserted into a groove. In an aspect, the buffer echoes bus signals having frequencies between 500 MHz. An overflow conduit 21 extends between an upper area of the first chamber 12 and a lower area of the second chamber 17 for equalizing gas pressure between the two chambers 12, 17.