By: Blonde Two
All good navigators know that magnetic north (where your compass points) is not usually the same direction as true north (direct line of longitude to the north pole). This means that grid north (the northy lines on a map) don’t match up exactly with what your compass says. To make things more complicated, magnetic north (mag) is a tricky creature to pin down and likes to move around.
When you are lost in the middle of a dark moor (and indeed, at most other times) it is difficult to remember what all of these “north words” mean. Most good navigators therefore, also know that when you take a bearing you add a couple of degrees (this varies according to your map but I just nudge mine a bit) if you are going from your map to the real world and take away a nudge of degrees if you are going from the real world to your map. Hence the saying “mag (magnetic north) to grid (map north) = get rid.”
Confused – me too, but doing it is a lot easier than explaining it. Anyway, things are about to get even trickier because naughty old magnetic north is on the move and has decided that being the other (west) side of true north is much more de-rigueur than that boring old east side.
The Ordnance Survey explain it here; http://www.ordnancesurvey.co.uk/blog/2014/01/magnetic-north-is-on-the-move-again/
I have no idea if I explained that right or not but I do know that we are going to need some new rhymes to help us to remember …
I do the same as you – just nudge on a couple of degrees ad lib, but really, I don’t think it is possible to walk accurately on a bearing to the nearest few degrees when you keep diverting the odd metre here and there for rough terrain. To do it accurately you would need to walk so slowly and carefully you would probably die of old age before you arrived at your objective, when most of the time you just want to make sure you are going arrive at that wall end or little tarn, and having visibility less than twenty metres is very rare, and if that is the case it is probably better to hunker down for a while and see if the viz. improves. We are not usually needing to be accurate enough to find a certain rabbit hole.
I will have to differ with you here. The Two Blondes have found themselves out in visibility less than 20m many times on Dartmoor and even more times in the dark. Legs are generally shorter when the conditions are like this however (navigation legs not our legs) and the deviation (which is minimal on Dartmoor) matters less.
We would probably eventually find the rabbit hole and, what is more, enjoy finding it. Watch this blog space for an exciting night time challenge!
You are probably right. I once set off from a Munro summit in thick mist. I took a bearing and walked in the direction of a half imagined point ahead on the bearing and put the compass in my pocket. Ten minutes later I found myself back at the summit cairn.
It is clever stuff that mist. Down here we have the pixies to deal with too!
My understanding, since being told in WGL training a few years ago, was that down on Dartmoor, the difference had been negligable for a few years and not actually worth making the correction.
Obviously, this was always going to change at some stage, is that now? What is the variation now?
Well that is an interesting question … in Princetown, the magnetic declination was 0º 51′ west in July 2013. In Penzance however, it was 0º 10′ west and is set to be eastish this summer!
Just be glad that the Earth isn’t imitating the Sun which has just had a complete polar change, so that its North is now its South and vice versa (mind you, the Sun does this exciting thing at regular intervals, so it won’t be confused.) With the variation being so slight do you need to take note of it at all ?
Hee – as I tripe this, the naked rambler has just appeared on telly. He says he has 2 compasses somewhere. That ain’t all he’s got!
I am not sure that you should be looking to see what else he has got! I wonder where he keeps his map.
Education, education, education ! Besides, I was away from school the wrek they did that in Biology.