In an embodiment, a power selective optical filter device includes an input polarizer for selectively transmitting an input signal. A biasing mechanism is configured to align a longitudinal axis of the body in a generally horizontal position extending away from the patient support. The memory includes cartographic data and a desired destination, the cartographic data including data indicative of thoroughfares of a plurality of types. The charge reservoir is connected to the voltage supply to provide a current through the resistive element.