How to Check for Local Declination Before Hiking?

Finding Local Declination Values

Declination values change over time due to the Earth’s magnetic field shifting. Check the most recent declination value for your location by consulting the United States Geological Survey (USGS) declination charts, which are updated annually. Alternatively, use an online declination calculator, such as the USGS’s Declination Calculator, which requires your location’s latitude and longitude. For example, if you are hiking in the Pacific Northwest region of the United States, the current declination value might be -12 degrees.

Understanding Declination and Magnetic North

Declination is the difference between magnetic north and true north. In most regions, magnetic north lies slightly south of true north. When navigating, it’s essential to set your compass to the local declination value to ensure accurate readings. A declination value of 10 degrees, for example, means that magnetic north is 10 degrees south of true north. Use a declination chart or calculator to determine the local declination value and set your compass accordingly. For instance, if you are hiking in a region with a declination value of 20 degrees east, set the declination bezel on your compass to +20 degrees.

Adjusting Your Compass for Declination

To adjust your compass for declination, locate the declination bezel on your compass, which is usually marked with degrees. If the declination value is positive (east), turn the bezel clockwise to set the correct declination value. If the declination value is negative (west), turn the bezel counterclockwise. For example, if you are hiking in a region with a declination value of -15 degrees, turn the declination bezel counterclockwise by 15 degrees to set the correct declination value.