What is magnetic declination or variation?
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What is magnetic declination or variation?

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A compass does not point to the true north - except by coincidence in some areas. The compass needle is attracted by magnetic force produced in the outer liquid part of the Earth's core, which varies in different parts of the world and is constantly changing. The magnetic north pole is currently located in the Baffin Island region of Canada, and from the UK, is west of true north. The direction in which the compass needle points is known as Magnetic North, and the angle between Magnetic North and the True North direction is called magnetic declination or variation.

The magnetic variation throughout Great Britain currently ranges from 2º to 6º. The level of variation changes with location as well as changing annually. This information is given on an Ordnance Survey map (see example below). It is therefore important to make sure that maps stay up to date. Ordnance Survey map showing Grid North, Magnetic North and True North variations for Purbeck UK, 1977 The diagram above shows a magnetic variation value of about 7°W for an Ordnance Survey map of Purbeck, UK in 1977. The value in 2013 is a little over 2° W.

Message to World Magnetic Model (WMM) Users NOAA/NCEI – March 21, 2018
The WMM Gridded Variation (GV) error has recently exceeded the performance specification in the Arctic region. Other geographic areas and other model parameters are not affected. The increased GV error may adversely affect compass navigation in those areas. This performance degradation is caused by fast changing core flows in the North polar region of the Earth’s outer core.