Quick Answer
In areas with high iron concentration, such as near steel factories or in areas with significant soil mineralization, a compass can be affected by magnetic interference. To use a compass effectively in these areas, identify the local magnetic variation and adjust for it. This may require significant declination corrections.
Understanding Local Magnetic Variation
Local magnetic variation, also known as declination, is the difference between magnetic north and true north. In areas with high iron concentration, this variation can be significant, often exceeding 10 degrees. To determine local declination, consult a reliable declination map or use an app on your smartphone. For extreme declination values, consider using a declination correction chart.
Compass Calibration Techniques
To compensate for local magnetic variation, perform a declination correction on your compass. Hold the compass level and rotate it until the magnetic needle aligns with the direction-of-travel arrow. Then, rotate the compass an additional amount to match the local declination value. For example, if the local declination is 15 degrees west, rotate the compass 15 degrees west of magnetic north. Repeat this process to ensure accurate navigation.
Field Testing and Verification
Before relying on your compass for critical navigation, test it in the field to verify its accuracy. Choose a recognizable landmark, such as a mountain or a ridge, and use your compass to determine the direction. Measure the distance to the landmark and verify that your compass indicates the correct direction. If your compass is off by more than a few degrees, recalibrate it using the techniques outlined above.
Find more answers
Browse the full Q&A library by topic, or jump back to the topic this question belongs to.