Dealing with Declination

[marty]

Hi all,

I recently took a map and compass class at REI last night to increase my modest knowledge on the topic. REI’s capable instructor taught the class how to manage declination (difference between magnetic true north) by drawing parallel lines on a map to align with magnetic north.

My previous practice has been to adjust my compass to align to true north, so it would be consistent with the map. The instructor advised against using the declination adjustment because people did not always set their declinations consistently, which could lead to problems when navigating as a group.

I have not decided whether I should change my previous practice or not and would greatly appreciate any advice that you can provide.

Many thanks,
Marty

 

[onestep]

Hi Marty,
I have a drawer full of maps with parallel magnetic north lines drawn on them. I've used this technique for a long time... works well!
Sometime during the past year or so I stopped drawing lines and started adjusting for declination on my compass. This too works well. I keep is simple though, I always use 15 degrees for declination and go with it. Close enough to get me to a New England summit and back.

 

[Pig Pen]

Keep in mind that if you adjust the declination on your compass, its no good outside of the Northeast, which might might be ok for you.

I just add 15 degrees to a true bearing to get a magnetic bearing. I can't hit a bearing within 1 degree anyway.

 

[Nessmuk]

Hi all,

I recently took a map and compass class at REI last night to increase my modest knowledge on the topic. REI’s capable instructor taught the class how to manage declination (difference between magnetic true north) by drawing parallel lines on a map to align with magnetic north.

I've been teaching the parallel line method in an Adirondack trek leader's course for nearly 20 years. Everyone should be aware of the compass adjustment method, but I think the line-on-map method is far superior for several reasons.

Perhaps the most important reason is the process of drawing lines gives you a chance to study the map in detail at home before you go. I'm a big proponent of pre-trip map study. It can save much grief in the woods, including being hopelessly lost if you lose the map entirely.

Parallel lines on a map do not lie - assuming you draw the first line correctly then it would be impossible to draw the other lines incorrectly. There is no guesswork in the woods with silly mnemonics like "east is least...." The general sanity check rule applicable anywhere in the lower 48 states is the lines should slant upward toward Chicago (where declination is zero). It is difficult to make a mistake in the woods when you have done all the calculation work at home.

The method uses the edge of your compass only as a protractor on the map. which means can use your compass on the map without regard to magnetic materials nearby. You can even put the map on the hood of your car at the trailhead to calculate a course with the compass. The rule I use is "whenever the compass is placed on the map, ignore the magnetic needle". The only exception to this is when you are at an area with a long visual view and you want to orient the map to the ground/true north to identify visible distant objects. In this case you simply rotate the map to align the parallel lines to the magnetic compass needle.

On the other hand, unless you do have a view, there is no reason to orient the map to ground/true at all for general navigation. Use the map and compass together on the move as you walk - no need to wait for the needle to settle down.

On older generation USGS topo maps there may not be a UTM grid overlay. Unless you want stop to go through the map-orient-to-ground exercise every time you want to make a measurement, you will have to draw lines of some kind. You might as well draw the lines at the declination angle.

The grid overlay is never more than 3 degrees away from true north, so you could use those lines and compass declination offset method. If you travel very far from home territory, don't forget to adjust the declination setting on the compass to the local value! But be sure to do the map study.

 

[Kevin Rooney]

Nessmuck - Maybe I'm dense, but ... do you adjust for declination or not?

 

[Nessmuk]

Nessmuck - Maybe I'm dense, but ... do you adjust for declination or not?

Of course I do. As I said above, I make the adjustment on the map with the parallel lines drawn at the declination angle. However, my compass dial always remains set to magnetic. The little screw on my compass is never adjusted from the default 000, so when I give you a heading from my compass it is always relative to magnetic north.

 

[Kevin Rooney]

Of course I do.

If it were clear I won't have asked...

 

[DougPaul]

I have not decided whether I should change my previous practice or not and would greatly appreciate any advice that you can provide.

IMO, it does not matter which method you use as long as you can do it correctly and reliably. The "pre-thought-out methods" (draw magnetic N-S lines on your map or use a declination adjustment on your compass) have the advantage that they require less thought out in the field.

FWIW, I use the declination adjustment on my compass and navigate using true N. I usually leave it set for my usual hiking area but am careful to reset it if I go elsewhere.

BTW, GPSes can be set to read out either magnetic or true headings.

Doug

 

[Papa Bear]

I have been using map and compass since forever. I guess I learned it in scouts in the 1950s.

Drawing lines on a map? Never did it. In fact I've never even seen anyone's map with lines drawn on it when I've gone whacking. Sounds unnecessary. I don't even have a compass with a declination adjustment. I just look at the map on Topozone before I go and remember 13 or 14 or 15 degrees. I'm up to that task.

The point is you ultimately want to internalize the idea and the methods so it's automatic. The methods discussed here seem fine for learning and I don't doubt the value of good teaching. However you need to be able to use any one's map, and one's compass, any time. Then you don't need to argue "this way is better" no "that way is better". Learn it so it's like walking. Who argues about which way to walk is better?

The lines drawn remind me of an old chorus director I had. We were singing some work in German. He got frustrated at our pronunciation and finally decreed that we had to cross out all the German words and write in English phonetic equivalent which he dictated. The method might have got us through the concert, but it certainly didn't help us read German.

So learn the basics of compass and map until you're a native speaker. As they say "How to I get to Carnegie Hall?" "Practice, practice, practice."

 

[Kevin Rooney]

IMO, it does not matter which method you use as long as you can do it correctly and reliably. The "pre-thought-out methods" (draw magnetic N-S lines on your map or use a declination adjustment on your compass) have the advantage that they require less thought out in the field.

FWIW, I use the declination adjustment on my compass and navigate using true N. I usually leave it set for my usual hiking area but am careful to reset it if I go elsewhere.

BTW, GPSes can be set to read out either magnetic or true headings.

Doug

Doug - I don't think it matters much either, so long as you're consistent. However, in terms of adjusting your compass for declination - I did that for a short period, but then a friend pointed out to me that it's not possible, at least for the brand/model I use, to tell whether the compass has been adjusted. It was a good point. I countered by suggesting putting a piece of tape on the bottom of the compass indicating the degrees of adjustment, but then he pointed out I wouldn't be able to see part of the map when the compass overlayed it. In short, I was convinced, and don't mess with the adjusting screw. Do you have some way of annotating your compass if it's been adjusted, or just remember that it has been and how many degrees?

 

[Nessmuk]

Doug - I don't think it matters much either, so long as you're consistent. However, in terms of adjusting your compass for declination - I did that for a short period, but then a friend pointed out to me that it's not possible, at least for the brand/model I use, to tell whether the compass has been adjusted.

?? What compass do you have? With any of the ordinary baseplate/bezel orienteering style compasses I have seen... if you adjust the declination screw, then the inscribed arrow on the bottom of the rotating bezel no longer points to "N" on the azimuth dial. It would be easy to tell with a quick glance that the compass has been adjusted.

I also agree it doesn't matter which declination adjustment method you use, basics are basics and if you have that knowledge you should be able to assume any of the methods with little trouble. Just pick one you like best.

 

[Peakbagr]

Agree with Nessmuk and others. I have always drawn parallel lines on all my maps.
Eliminates mechanical error with on on-compass adjustment and also eliminates the different declinations for maps from different parts of the country.
I typically don't use other peoples maps and if I do, remember to use the proper declination offset for the area I'm travelling.

 

[DougPaul]

Do you have some way of annotating your compass if it's been adjusted, or just remember that it has been and how many degrees?

On my compass (Silva Ranger CL, similar to http://www.rei.com/product/408031) I can simply read the setting from the pointer. (You need to be able read the setting to be able to adjust it too.)

Seems odd to me that a compass would be designed in a way in which one cannot read the declination setting.

Doug

 

[Kevin Rooney]

On my compass (Silva Ranger CL, similar to http://www.rei.com/product/408031) I can simply read the setting from the pointer. (You need to be able read the setting to be able to adjust it too.)

Seems odd to me that a compass would be designed in a way in which one cannot read the declination setting.

Doug

Well, odd or not, you cannot. IIRC it's a Sunnto. It's my 'backup' compass, so I rarely use it.

 

[DougPaul]

Well, odd or not, you cannot. IIRC it's a Sunnto. It's my 'backup' compass, so I rarely use it.

IMO, a hazardous flaw in its design.

How do you set it, if you cannot read out the setting?

Doug

 

[Peakbagr]

I have 2 Rangers. I don't use the compass adjustments to avoid introducing human error(easily mine) or equipment breakdown into the equation. From Army days and 3 decades of whacking, doing the map table homework with drawn lines parallel to the maps declination line is how its always worked for my purposes.
My Garmin 60CSx makes it so easy to get lazy, that I still draw my bearings and bring the map(s).

 

[Kevin Rooney]

IMO, a hazardous flaw in its design.

How do you set it, if you cannot read out the setting?

Doug

I would agree that it's a design flaw. I reset it by carefully comparing it with 2 other compasses, both of which were in agreement with each other.

So now I have 3 compasses which are correct. Or 3 that are all off by the same error ...

 

[dentonfabrics]

You may remember that back in the 1960s, the Tates Compass Company was brought down by a class action law suit among hikers and outdoorsmen. They proved in court that the Tates Compass was absolutely unreliable. Thus, the saying was born, He Who Has A Tates Is Lost.
.
.
.
.
.
.
.
sorry, couldnt help myself

 

[HH1]

Kevin,

If you set your dial to read a bearing of 360 (0) degrees, then rotate your compass to magnetic north (ie. the needle is placed inside the orienting arrow), the angular difference between where the needle points and the 360 degree mark on your dial is the declination setting dialled into your compass.

If, for instance, the needle is pointing to the 345 degree mark on the dial, then your compass is set to approximately 15 degrees west declination.

As others have pointed out, there is usually a declination setting feature in the compass, one that permits a rotation of the orienting arrow relative to the dial's north-south lines, that allows a much more precise setting of declination.

 

[Chip]

I reset it by carefully comparing it with 2 other compasses, both of which were in agreement with each other.

Sorry, couldn't resist;

Vinny Gambini: [Vinny hears a drip in the motel bathroom] Weren't you the last one to use the bathroom?
Lisa: So?
Vinny Gambini: Well, did you use the faucet?
Lisa: Yeah.
Vinny Gambini: Then why didn'tcha turn it off?
Lisa: I DID turn it off!
Vinny Gambini: Well, if you turned it off, why am I listening to it?
Lisa: Did it ever occur to you it could be turned off AND drip at the same time?
Vinny Gambini: No. Because if you'd turned it off, it wouldn't drip!
Lisa: Maybe it's broken.
Vinny Gambini: Is that what you're saying? It's broken?
Lisa: Yeah. That's it, it's broken.
Vinny Gambini: You sure?
Lisa: I'm positive.
Vinny Gambini: Maybe you didn't twist it hard enough.
Lisa: I twisted it just right.
Vinny Gambini: How could you be so sure?
Lisa: [sighs] If you will look in the manual, you will see that this particular model faucet requires a range of 10 to 16 foot-pounds of torque. I routinely twist the maximum allowable torquage.
Vinny Gambini: Well, how could you be sure you used 16 foot-pounds of torque?
Lisa: Because I used a Craftsman model 1019 Laboratory Edition Signature Series torque wrench. The kind used by Caltech high energy physicists. And NASA engineers.
Vinny Gambini: Well, in that case, how can you be sure THAT's accurate?
Lisa: Because a split second before the torque wrench was applied to the faucet handle, it had been calibrated by top members of the state AND federal Department of Weights and Measures... to be dead on balls accurate!
[She rips a page out of a magazine and hands it to him]
Lisa: Here's the certificate of validation.
Vinny Gambini: Dead on balls accurate?
Lisa: It's an industry term.
Vinny Gambini: [tosses paper away] I guess the ******* thing is broken.