In accordance with an embodiment, a modulator includes a comparator and ramp generating circuitry. In response, a user is prompted to cause an update to their registration andor location information. A whistle is attached to the arrow body. The end wall portions have inner surfaces of constant or smaller varying radii of curvature and they are separated from the interior ends of the electrodes by more than one millimeter. The auxiliary magnet is to rectify the magnetic flux pattern outside the end pole of the field magnet to the same distribution pattern as found at a boundary between the adjacent poles opposite in polarity in the field magnet, thus making it possible to identify the accurate positions of the forward and aft end pole of the field magnet.