Have I got this declination adjustment right?

[nsherry61]

. . . I've got it set between 13 and 14, and hopefully over the distance I'm going, the difference will be negligible enough... HOPEFULLY!!!

If you can navigate more precisely than the 2* spacing between hash marks on most compass bezels, you're doing way better than most of us.

[Kenai]

Here's a piece I posted some time ago that gives both the math subtraction and the compass-offset method for dealing with declination - maybe it will help

http://artofwayfinding.blogspot.com/...ling-with.html

Thanks for the great article John Huth. I went on to read your "Art of Wayfinding" article. The visual representations made the text crystal clear to me. Been a long time since orienteering with the Boy Scouts. I hope this does not become a lost art. It will be tough for a great many to find their way without their 4G LTE smartphones.

[egilbe]

To throw another wrench into it, Magnetic North tends to wander a bit. Depending on how old your maps are, they may no longer be accurate. The only time I can think one would need to be really accurate is when calling artillery fire onto a target. Other than that, the general area is usually good enough.

[jefals]

To throw another wrench into it, Magnetic North tends to wander a bit. Depending on how old your maps are, they may no longer be accurate. The only time I can think one would need to be really accurate is when calling artillery fire onto a target. Other than that, the general area is usually good enough.

Thanks egilbe. I think they try to keep the artillery fire to a minimum out there, so I should be good!

[rickb]

To throw another wrench into it, Magnetic North tends to wander a bit. Depending on how old your maps are, they may no longer be accurate. The only time I can think one would need to be really accurate is when calling artillery fire onto a target. Other than that, the general area is usually good enough.

Assuming your team of patriots is like those I watched on the latest Red Dawn movie, I think I would just gather everyone together in advance and agree to use Magnetic North for all communications.

And that they can just orient their maps to the arrow that says "Magnetic North".

[egilbe]

Thanks egilbe. I think they try to keep the artillery fire to a minimum out there, so I should be good!

I had to learn how to do it and that's how I leaned how to use a map and compass.

[nsherry61]

Gosh, while we're working to get complicated. Another functional alternative to adjusting declination on your compass is to draw a whole new set grid lines on your maps oriented to magnetic north. Then you can ignore the declination adjustment on your compass and the true north grid lines on your map.

[JohnHuth]

A few quick points -

If you're hiking in the northeastern US and use the 'offset' of the magnetic needle, you'll want that pointing to the 'west' on the dial to compensate for declination. In Boston, it's about 16 degrees west, so I line up the needle with 344 degrees (noting that my precision is rarely better than 2-3 degrees). If I'm hiking in Washington State, where the declination is about 16 degrees east, I line up the needle to the east of the arrow on the housing - so it's pointing to 16 degrees. Since I hike regularly in the east coast, the times when I do hike on the west coast, I always have to pause and remind myself.

The add/subtract trick works, too and I know some people who prefer this - not a big deal, but find a method that works for you and stick with it. I frequently just do both to be methodical.

The secular (time-based) change is typically quite slow, so unless the maps you use are ancient, the declinations on those maps are probably good enough.

I've used compasses the most when I bushwhack, but I carry one when I'm on a trail in any case. Sometimes when you come to a confusing trail junction, the map and compass can help you resolve which way you want to go.

Another time, I was hiking an area where there were few water sources, save for springs every 6-7 miles apart. The area was confusing and I didn't want to miss the next spring, so I used triangulation to gauge my location and progress.

There's more stuff you can link to from that post - it was mainly intended for sea kayakers, but a lot of it works for backpackers.

For the savant, you might want to check out the animation of the time variation of the magnetic field of the earth on this website:

http://www.geo.arizona.edu/palynolog...2paleomag.html

you need to scroll down - it shows you the change in magnetic declination (variation) from 1560 to present across the earth.

[JohnHuth]

Gosh, while we're working to get complicated. Another functional alternative to adjusting declination on your compass is to draw a whole new set grid lines on your maps oriented to magnetic north. Then you can ignore the declination adjustment on your compass and the true north grid lines on your map.

I do this myself. Here's another post in that series that shows you how to do it on a nautical chart, but the switch-over to a topographic map is quite easy. Note that I make the line spacing a mile - so you can lay out the lanyard in the compass over a path, pull it straight and quickly get a distance.

http://artofwayfinding.blogspot.com/...ion-lines.html

[jefals]

Gosh, while we're working to get complicated. Another functional alternative to adjusting declination on your compass is to draw a whole new set grid lines on your maps oriented to magnetic north. Then you can ignore the declination adjustment on your compass and the true north grid lines on your map.

Yes, I saw that in one of the videos I watched. Didn't seem too difficult either way. btw, the light came on for me, last night while I was kinda half sleeping. My confusion was that, since I was already 13 degrees east with no adjustment for declination, I thought it made sense to adjust the arrow towards the west. But it finally dawned on me that, by adjusting to the east, I now have to turn the body of the compass towards the west to get the "red in the shed".

[jefals]

I had to learn how to do it and that's how I leaned how to use a map and compass.

Well, you got me thinking about artillary fire, and thinking about the times we live in, and this awesome place I'm hiking in -- and I hate do digress from the purpose of this forum, but God Bless the brave young men and women keeping us and our families safe and free in this amazing land!

[Dogwood]

I stick to only hiking within about 50 miles of the Mississippi River. N need to learn about MD.

[jefals]

A few quick points -

If you're hiking in the northeastern US and use the 'offset' of the magnetic needle, you'll want that pointing to the 'west' on the dial to compensate for declination. In Boston, it's about 16 degrees west, so I line up the needle with 344 degrees (noting that my precision is rarely better than 2-3 degrees). If I'm hiking in Washington State, where the declination is about 16 degrees east, I line up the needle to the east of the arrow on the housing - so it's pointing to 16 degrees. Since I hike regularly in the east coast, the times when I do hike on the west coast, I always have to pause and remind myself.

Yes, that's what I was having a hard time with. I was thinking that I should be adjusting in the opposite direction of the declination. I figured, if my compass is already pointing too far east, I want to adjust it towards the west. It finally dawned on me that the needle's going to keep pointing in the same direction, no matter what adjustment I make. The adjustment to the east, forces me to turn the housing to the west --- so that's why everything works out!!

The add/subtract trick works, too and I know some people who prefer this - not a big deal, but find a method that works for you and stick with it. I frequently just do both to be methodical.

I'm kinda thinking this might leave me more prone to mistakes. I can set my declination and plot my course well ahead of time.
One thing novices (like me) should probably be reminded of is that you're going to have to be aware if you're trying to plot your course ahead of time using your map and compass -- while you are, say, in Boston, and planning a hike in Washington State. That's gonna add a little complexity, since you're going to have to adjust for the declination in both places....right?

The secular (time-based) change is typically quite slow, so unless the maps you use are ancient, the declinations on those maps are probably good enough.

I've used compasses the most when I bushwhack, but I carry one when I'm on a trail in any case. Sometimes when you come to a confusing trail junction, the map and compass can help you resolve which way you want to go.

I'm not sure what bushwhacking is. THe mental image I get is someone with a machete, hacking their way thru a jungle. But off-trail, in any case. That's why I'm interested in it -- trying to stay on a trail, where the trail disappears and then picks up again on the other side of granite fields...

[JohnHuth]

Yes, it's generally good to think about how you're going to approach things ahead of time. I was on Colorado where the declination was 8 degrees *east* and I started taking a bearing assuming a *west* declination, but caught myself in the process.

Also - it's pretty common to go through the thought process you did - thinking of compensating in the opposite direction. At the base of most topographic maps, there's a little arrow offset to show declination - that's what the compass orientation should look like to compensate properly. You aren't the only one who gets confused - there's the story of Steven Whittaker who decided to cross Nova Scotia via canoe and on foot. He got the 18 degree declination backwards and ended up getting horribly lost. In effect, he was traveling 36 degrees off of what his heading should have been.

"Bushwhacking" - has different meanings, I guess. It does have a connotation of hacking brush, but it also has a meaning of going off-trail, for me and the people I go out with anyway. That's a good exercise in and of itself.

If you want to hone your skills, you might want to see if you can find a local orienteering club and run (or walk) one of their courses. I frequently take people out into some local woods and once they're comfortable, have them take an old course - it adds some comfort level. Like most skills, practice is important, and getting good feedback - making mistakes, correcting them, etc will give you confidence.

[jefals]

Thanks John. I may look for an orienteering club. Didn't think of that and it's a good idea.
Yeah, I know about the little diagram. One youtube I watched, the fellow had his compass under the diagram, with the North cardinal indicator under TN and the shed pointing in the direction of MN. He made the point that you should really redraw this diagram first, or at least check it, with a protractor.

[nsherry61]

. . . One thing novices (like me) should probably be reminded of is that you're going to have to be aware if you're trying to plot your course ahead of time using your map and compass -- while you are, say, in Boston, and planning a hike in Washington State. That's gonna add a little complexity, since you're going to have to adjust for the declination in both places....right? . . .

Actually, wrong.

Declination only matters when you are in the field trying to orient yourself and your map to magnetic north. When plotting headings on a map, if you use your compass, you are only using it as a protractor. You can be facing any direction you want. Your heading is calculated off the the map grid lines, not a magnetic compass heading. . . I hope.

[jefals]

Actually, wrong.

Declination only matters when you are in the field trying to orient yourself and your map to magnetic north. When plotting headings on a map, if you use your compass, you are only using it as a protractor. You can be facing any direction you want. Your heading is calculated off the the map grid lines, not a magnetic compass heading. . . I hope.

Thanks, Nsherry -- you might have just saved my life! Just doublechecked this, and discovered you are correct -- changing the declination is NOT changing the outer ring of my compass.

[MuddyWaters]

Only thing you need declination for is orienting a map, and absolute measurements from true north.

to orient map. lay on ground, align compass with N-S lines, and rotate map until needle points to declination on declination scale. Now it matches orientation of real world.

Shooting bearings, plotting on map, etc are all relative measurements. They can be relative to true or magnetic north. You can use either

One is easier because thats where the compass points and requires no math.
Just be consistent.

[rickb]

One is easier because thats where the compass points and requires no math.
Just be consistent.

Probably why the thumb compasses they uses for orienteering competitions don't adjust for declination.

[fudgefoot]

Probably why the thumb compasses they uses for orienteering competitions don't adjust for declination.

Orienteering maps are always drawing to magnetic north so there is no need to correct for declination. Saves a lot of time when trying to navigate during a race.