To correct for declination when using a compass, you need to adjust your compass reading to account for the difference between true north and magnetic north. This process involves either adding or subtracting the declination value, which varies by location and changes over time.
What is Magnetic Declination?
Magnetic declination is the angle difference between true north (geographic north) and magnetic north. This variation occurs because the Earth’s magnetic field is not aligned perfectly with its rotational axis. Declination values can range from 0° to over 20°, either east or west, depending on your location.
Why is Correcting for Declination Important?
Correcting for declination is crucial for accurate navigation. Without this adjustment, your compass readings could lead you off course. For instance, if you are hiking in an area with a 10° east declination and you do not adjust your compass, you could be significantly off your intended path over long distances.
How to Find Local Declination?
To find the local declination:
- Check Topographic Maps: Most topographic maps include the local declination value, often found in the map legend.
- Use Online Tools: Websites like the National Oceanic and Atmospheric Administration (NOAA) provide updated declination values based on your geographic location.
- Smartphone Apps: Several apps can calculate declination using GPS data.
Steps to Correct for Declination on a Compass
1. Determine the Declination Value
Before you set out, determine the current declination for your location. This value will guide whether you need to add or subtract from your compass reading.
2. Adjust Your Compass
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For East Declination: Subtract the declination value from your compass bearing. For example, if your map bearing is 45° and the declination is 10° east, adjust your compass to 35°.
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For West Declination: Add the declination value to your compass bearing. For example, if your map bearing is 45° and the declination is 10° west, adjust your compass to 55°.
3. Use the Compass with Adjusted Bearings
Once adjusted, use your compass to navigate. This ensures that your path aligns with true north, minimizing navigational errors.
Practical Example
Imagine you’re navigating in Denver, Colorado, where the declination is approximately 7° east. If your desired bearing from a map is 90° (due east), you would subtract 7° from your compass reading, setting it to 83° to align with true north.
People Also Ask
What is the difference between true north and magnetic north?
True north refers to the direction along the Earth’s surface towards the geographic North Pole. Magnetic north is the direction a compass needle points, towards the magnetic North Pole. The difference between these two directions is the magnetic declination.
How often does magnetic declination change?
Magnetic declination changes over time due to shifts in the Earth’s magnetic field. It can change slightly each year, so it’s important to use updated maps or tools to find the current declination for your location.
Can declination be zero?
Yes, declination can be zero in certain locations where true north and magnetic north align. In these areas, no adjustment is needed when using a compass.
How do I adjust a compass with a built-in declination adjustment?
Some compasses have a built-in declination adjustment feature. To use this, turn the declination adjustment screw or dial to set the local declination value. This allows the compass needle to automatically point to true north without manual calculation.
Are there any tools to help with declination correction?
Yes, many modern GPS devices and smartphone apps automatically account for magnetic declination, providing users with bearings aligned to true north. These tools are especially useful for those who frequently navigate in different regions.
Conclusion
Correcting for magnetic declination is essential for accurate navigation with a compass. By understanding how to find and adjust for declination, you can ensure your path aligns with true north, reducing the risk of navigational errors. Whether you’re hiking, orienteering, or exploring new territories, mastering declination correction enhances your outdoor navigation skills.
For further insights on navigation techniques, consider exploring topics like "how to read topographic maps" or "using GPS for hiking."
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