Quick Answer
You should recalculate declination at the start and end of each day, and also when you cross into a new region with different declination values, ideally every 200-400 miles.
Importance of Declination
Declination, also known as magnetic variation, is a critical factor in navigation that can lead to significant errors if not accounted for. As you hike, your compass will not point directly to the geographic North Pole, but rather to the Magnetic North Pole, which can be several degrees away. If you’re using a map and compass for navigation, it’s essential to know the declination value for your area to ensure accurate readings.
Recalculating Declination
To recalculate declination, you can either use a declination chart or consult an online resource. For example, the United States Geological Survey (USGS) provides declination values for various locations in the United States. If you’re planning a multi-day hike, it’s a good idea to calculate the declination for each day’s route and note it down in your journal or on a sticky note. This way, you can quickly reference the correct declination value when making navigation decisions.
Declination in Practice
When recalculating declination, make sure to use the correct value for your location and date. Declination values can change over time, typically by about 1-2 degrees per year. To account for this, you can use a declination correction chart or consult with a local expert. Additionally, if you’re using a GPS device, it’s essential to set the declination value correctly, as many devices will automatically adjust their readings based on the entered value.
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