Quick Answer
To adjust your course for magnetic declination, you need to add or subtract the declination value from your compass reading, depending on whether you're in a region with a positive or negative declination. This ensures your compass direction aligns with true north. Use a declination chart or app to find the value for your location.
Understanding Magnetic Declination
Magnetic declination is the difference between magnetic north and true north. It varies depending on your location and the Earth’s magnetic field. A declination chart or app will provide you with the declination value for your area. For example, if you’re in the northern United States, the declination might be around +10 degrees east.
Calculating Course Corrections
To adjust your course, add or subtract the declination value from your compass reading. If the declination is positive, add the value to your north-south bearing. If it’s negative, subtract the value. For example, if your compass reading is 270 degrees (due south) and the declination is +10 degrees, your true course would be 260 degrees. Conversely, if the declination is -10 degrees, your true course would be 280 degrees.
Plotting Adjusted Courses on Maps
When plotting your course on a topographic map, use the adjusted bearing to ensure you’re heading in the correct direction. Use a protractor or a compass rose to draw a line representing your course. Double-check your calculations and bearings to ensure accuracy. In areas with significant declination, it’s essential to make these adjustments to avoid getting lost or disoriented.
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