Operation In Urban Areas

The electronic compass, like any compass, is influenced by external magnetic fields. In order to shut out as much external magnetic interference as possible, the compass has filters programmed into it which vary depending on vehicle speed. These filters relate the vehicle speed to the time in which the vehicle could conceivably change directions. The filters correspond to speeds between 0 and 16 km/h (0 and 10 mph), between 16 and 64 km/h (10 and 40 mph), and above 64 km/h (40 mph). They take into account that at higher vehicle speeds, the vehicle should not be able to significantly change direction as quickly as at lower speeds. These filters are used to help avoid false readings due to the influences of external magnetic fields. Such fields may exist in areas where there are large steel structures, such as skyscrapers, bridges, roads with steel reinforcement, railroad tracks, etc. If the field projected by these external influences represents too drastic a change of direction for the conditions, no change to the displayed direction should occur. However, under borderline conditions, as in large cities with slow driving, the compass may give false readings and appear to be malfunctioning. The compass should be taken to an open area, free from magnetic disturbances, to be checked.