I’ve been considering the implications for dinosaurs like me, who still prefer to navigate by map and compass, now that grid magnetic north in the the extreme west of Cornwall is now east of grid north. No longer can we rely on the mnemonic ‘Add for mag; get rid for grid’ that Captain Paranoia rightly despises. I fear that some walkers may get confused.
For some years I’ve ignored the difference between magnetic north and grid north when navigating in lowland countryside both at night and in any weather conditions. I take the view that as most compasses mark degrees in 2° increments; the grid magnetic angle is rarely more than 3°; and the distances over which I take bearings are usually less than 500 metres means that the inherent inaccuracy is acceptable.
According to the British Geological Survey website mentioned by Hobbo, in July 2014 the differences between magnetic north and grid north rounded to the nearest degree will be
Penzance (the most westerly town in mainland Great Britain) 1° E
Lowestoft (the most easterly town in mainland Great Britain) 3°W
This simplified method has worked so well that I’ve adopted the same technique when navigating in upland areas in good conditions. When the weather is foul and visibility is poor, or circumstances require maximum precision, I adopt the standard recommended procedure. Needless to say, I do not teach this method in navigation classes.
I’d be interested in reactions from any fellow-dinosaurs amongst the members of this forum.
Hugh