A method and apparatus for presenting three-dimensional data to a physician is provided to facilitate the flexible navigation of an endoscope and surgical instruments with respect to anatomical structures. Based on the magnetic field profile, the device may detect any unacceptable irregularities in the magnetic field and identify a location of the cylindrical magnet associated with the irregularity. A primary discharge slot at the end of the rake face cooling channel delivers fluid from below the cutting edge of the insert. An insert for a windshield assembly is also disclosed. The router then drops packets transmitted by the first computer system when the packets were transmitted subsequent to the receipt of the marked packet. One or more disruptions are introduced into a pre-selected airline flight schedule, using frequency distributions of disruptions and disruption severities, resulting in a disrupted flight schedule that reflects both initial and propagated delays.