An apparatus for traversing obstacles having an elongated, round, flexible body that includes a plurality of articulating propulsion members. This accessory comprises an attachment operable to attach to a power source on one end and a quick release chuck andor a keyless chuck on the opposite end that allows a wide range of drilling devices to be attached. A plurality of wireless service plans that meet the wireless preferences and are offered by a plurality of wireless carriers that provide service to the geographic location are determined. The first tunneling barrier has a MR ratio that differs from a MR ratio of the second tunneling barrier. The present invention also includes a method for word-line patterning of a non-volatile memory array which includes generating sub-F word lines from mask generated elements with widths of at least a minimum feature size F. The length of time between two passages of teeth is calculated by interpolating the cross-correlation function using least squares interpolation.