The $39, non-electrical, non-computerized device – registered for an international patent – appears to defy nature, as the magnetic needle does not always point north. It is pre-calibrated for the continental US (excluding Miami, Hawaii and Alaska). But “log book” code numbers on the inside of the brass cover encompass virtually any other location on the globe. The user recalibrates by releasing the MPR bar, rotating the rim of the compass glass until the needle is opposite the relevant code number on the dial and sliding the MPR bar towards him after recalibration. The setting doesn’t have to be changed until you travel to another city in a large country or a different small country.
Got it. 🙂