1997 Pontiac Bonneville Owner's Manual - Page 138

Compass Accuracy Your compass may showdifferent headings around bridges, power lines, large metal objects and steep hills. This is normal and is true of compasses in general. If you put large metal objects like golf clubs in the trunk If they could affect accuracy. the accuracy is close, the compass will adapt to these objects over time. If you use an antenna with a magnetic base, it is best to mount it away from the center of the trunk near the rear window. The rear defog system can affect accuracy, and the compass corrects for the rear defog. However, if the rear defog is turned on while making sharp turns, the accuracy may be off. When you turn the rear defog off again, the accuracy returns to normal. Do not turn on the rear defog if you are trying to calibrate, The system will not allow the calibration. You will hear the chime, and CALIBRATE willflash for a few seconds. Be aware that metal objects are sometimes buried inthe ground. They can affect accuracy and you may notknow they are there. As an example, many concrete roads have metal reinforcements inside. 2-85