Quick Answer
Ignoring compass declination adjustments can lead to navigation errors of up to 30 miles per day, significantly impacting the accuracy of your route.
Understanding the Dangers of Compass Declination
Compass declination, also known as magnetic declination, is the difference between a compass’s magnetic needle and the Earth’s magnetic field lines. It varies depending on your location and changes over time. If you’re not accounting for declination, your compass readings will be offset by the difference between the local magnetic field and the Earth’s magnetic field lines.
Calculating Compass Declination
To adjust for declination, you need to know the current declination value for your location. The National Geophysical Data Center (NGDC) publishes declination values for different regions. You can also use an online declination calculator or consult a local map to find the declination value for your area. For example, if the declination is 10 degrees east, you need to add 10 degrees to your compass readings to get an accurate bearing.
Applying Declination Adjustments in the Field
When using a compass for navigation, it’s essential to apply the declination adjustments to get an accurate bearing. This means adding or subtracting the declination value from your compass reading. For instance, if you need to head 270 degrees (west) but the declination is 10 degrees east, your adjusted bearing would be 260 degrees. Failing to apply declination adjustments can lead to navigation errors, especially over long distances or in unfamiliar terrain.
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