Quick Answer
If your compass reads incorrectly, adjust for declination by using a declination chart or map to determine the variation in your area, and then adjust the compass by subtracting the east/west variation or adding the north/south variation, according to the chart's instructions.
Understanding Compass Declination
Compass declination occurs when the compass needle does not align with the Earth’s magnetic poles due to variations in the Earth’s magnetic field. These variations are caused by the movement of molten iron in the Earth’s core. As a result, the compass needle will deviate from true north, leading to incorrect readings.
Calculating Declination
To adjust for declination, you need to determine the variation in your area. Use a declination chart or consult a map to find the declination for your location. The chart will provide the variation in either east-west or north-south direction, depending on the specific location. For example, a chart may show a variation of 10° E (east) or 5° S (south). This means that if you are in an area with a 10° E variation, you need to subtract 10° from your compass reading to get true north.
Adjusting Your Compass
Once you have determined the declination for your area, adjust your compass accordingly. If the variation is east-west, subtract the variation from your compass reading to get true north. If the variation is north-south, add the variation to your compass reading. For example, if your compass reads 350° and the variation is 10° E, adjust the reading by subtracting 10° to get 340°, which is true north. Alternatively, if your compass reads 30° and the variation is 5° S, add 5° to get 35°, which is true north.
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