Physical requirement, Palm Pilot original, Palm III style devices. This device attaches to the Palm device using the accessory "pits" at the bottom of the housing. From the Readme.txt:

The Palm Navigator combines a magnetic sensor module with advanced software that turns your Palm Pilot into a hand-held map-based navigation system. The Palm Navigator utilizes patented magnetic sensing technology to measure the earth's magnetic field to determine heading information that is used to show the direction you are facing. Your heading can be displayed like a convention compass or combined with a map to give you a powerful navigational tool. This is the same sensor technology that was developed for the U.S. military, and is now or will be used in Ford, GM and Chrysler cars, Bayliner boats, Polaris jet skis, Motorguide trolling motors, Oceanic scuba compasses, and Timex compass watches.

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