For those using Compass watches, Compass Declination may be essential for accuracy.
Magnetic Declination is the angular difference between the Magnetic North Pole and the True North pole. The amount (degrees and minutes) and direction (easterly and westerly) depends on where you are in the world. For accurate navigation the compass must be adjusted to include the magnetic declination.
Often compass watch wearers ignore magnetic declination as their particular watch compass accuracy may typically be no better than +/- 10°, though depending on location some declinations can be relatively large, so my personal preference is to use the adjust for declination on those few occasions I have use for the compass feature on my watch. My own personal experience with compass watches is that they are a useful “rough guide” at best and no substitute for map and dedicated compass or GPS hybrid technology today. I have not included figures or charts here as the Declination figures have once again altered. For example a couple of years ago at my home location it was -2.9º West and today this is now -1.3ºW, so it’s best to search online for a 2015 calculation page for the current figure for your location or intended location for use.
However if in a part of the world where the declination is large then it is sensible to adjust for it – the table shows the your track deviation after 10 miles with different degrees of declination.
Not that I’d walk 10 miles between compass checks! If in dense cover country even 100 metres can make a difference so frequent heading/bearing checking should be the norm.
Here in the UK I have set my adjustment for -1º West on all my compass watches (those that allow it). Another tip is to make sure if compass orienteering, to have an up to date current map. An old one will definitely have the wrong declination set printed on it, which won’t do you any good at all.
There’s no doubt that GPS is probably the way I’ll go in the future, but not at this time. Basically as GPS models required for trekking and so on are far too large, battery hungry and still in my opinion, feeling their way in the technology, with the buyer in the front line as tester and financial supporter!
Until they get some of the basics sorted out, I’ll stick to my compass or ABC model and I’ll still carry my map.