A sentence using magnetic declination

Your magnetic compass does not actually point north, it merely aligns itself with the lines of magnetic force at your location. These do not necessarily point to the North - they may differ by some tens of degrees. This difference is the Magnetic Declination.

On hikers maps, you'll find that the true north of the map is shown as well as the magnetic declination at that region. The declination itself changes slowly, too slow for you to bother with its changing.