Quick Answer
Compass declination varies across the United States, with differences ranging from a few degrees to over 30 degrees depending on the location.
Understanding Compass Declination
Compass declination, also known as magnetic declination, is the difference between magnetic north and true north. This variation is caused by the Earth’s magnetic field and can change over time due to movements in the Earth’s magnetic poles. In the US, declination ranges from -32.6 degrees in Alaska to +23.2 degrees in the state of Maine.
Calculating Compass Declination
To determine the compass declination for a specific location, you need to know the longitude and latitude of that place. The US Geological Survey (USGS) provides declination values for various regions, which can be found online. You can also use a declination chart or app that provides the current declination value for a given location. For example, at 40.7128° N latitude and 74.0060° W longitude, which is New York City, the current declination value is +11.4 degrees.
Correcting for Compass Declination
To ensure accurate navigation, you need to correct for compass declination. This can be done by applying a correction to your compass reading. In the case of a compass with a rotating bezel, you would rotate the bezel to the correct declination value. If you’re using a digital compass, you would enter the declination value into the device. By correcting for compass declination, you can ensure that your compass readings are accurate and align with your map coordinates.
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