How should magnetic bearing be adjusted when there are changes in magnetic declination?

When there are changes in magnetic declination, it is essential to understand how these changes affect the accuracy of magnetic bearings. Magnetic declination is the angle between magnetic north (the direction the compass needle points) and true north (geodetic north).

In cases where the magnetic declination is east of true north, the magnetic north is actually pointing towards true north, which means you need to correct the magnetic bearing to provide a true bearing. This correction involves subtracting the declination value from the magnetic bearing.

For instance, if you have a magnetic bearing of 60 degrees and the magnetic declination is 10 degrees east, subtracting the declination to convert to true bearing gives you a true bearing of 50 degrees.

Understanding this adjustment is crucial for accuracy in navigational tasks and ensures that the bearings used in geodetic engineering surveys align with the true geographic positions. Therefore, to maintain accuracy in measurements and positioning, the correct approach is to subtract the declination value from the magnetic bearing.