Re: Declination/Magnetic Variation
- From: Peter Clinch <p.j.clinch@xxxxxxxxxxxx>
- Date: Mon, 01 May 2006 16:50:41 +0100
Jim Ford wrote:
Taken from "Mountain Navigation", by Peter Cliff. There's a couple of others in there, but, ummm, I can't remember them! ;-/
I've never really felt the need to fiddle around with the couple of degrees difference between mag North and grid North.
It's changed over time, and probably also changes according to where you are in the grid to some extent: when I started map reading as a Scout it was about 7.5 degrees, which *is* worth accounting for!
whether you can take a bearing with a Silva type compass accurate to within 2 degrees anyway - to do any better you'd need a prismatic compass.
My compass is a Silva with a sighting prism too, the 54 NL, though to be honest I don't use the sighting feature much. Most often I walk on very approximate bearings (like "just to the left of North") where I don't correct. If you can keep track of where you are that's usually quite good enough, and orineteers' thumb compasses don't allow any better than that.
As long as I'm carrying enough food and have shelter, I'm not particularly bothered with compass navigation. I've ended up in interesting places on the occasions when I've got lost!
Often the case, but if just wandering along until you get to some known point takes you out onto a collapsing cornice it could Ruin Your Whole Day... The descent from the top of Ben Nevis in clag is a prime example that's cost peoples lives when they got it wrong.
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net p.j.clinch@xxxxxxxxxxxx http://www.dundee.ac.uk/~pjclinch/