Question About Declination

[Kevin Judy and Emma]

This question was posted over at the MWOBS Forum and so far has not been answered. All I know about the subject is that there is a 17 degree westerly declination. I'm sure this has been discussed here before, if someone could point me to the thread or give an explanation, I'm sure it would be appreciated. I'm sure with the wealth of knowledge here someone will know how to answer this. The question is as follows:

All right. This question is for all you compass savvy travelers out there. First off, I don't have a GPS nor will I be purchasing one anytime soon. I do however have a nice Silva Ranger orienteering compass with a built in gear to permanently set the declination. Secondly, I understand the basics of compass use and would not have a problem navigating. I have used compasses to steer my way up munroes covered in thick fog in Scotland countless times.

My question is geared more towards my confusion of some explanations found in "Freedom for the Hills" 7th edition and my Silva compass manual. I will quote these explanations/instructions for your benefit. Perhaps you even have this book and model of compass yourself, which would make you even more qualified to assist me.

Now, I understand that we who live on the East coast of the U.S. or East of the line of 0 declination or "agonic line" would be described as having to use a Westerly declination. On one of my maps of N.H. it says that there is a 17degree westerly declination. For those living on the West coast, they would have an Easterly declination as magnetic north is somewhere to the East of true North. Ok, that I get, what I don't get is the following explanations.

Taken from "Freedom of the Hills" page 95 in the chapter on navigation

"In areas WEST of the line of zero declination, the magnetic needle points somewhere to the EAST (to the right) of True North. So, these areas are said to have EAST declination. It works just the opposite on the other side of the line of zero declination, where the magnetic needle points somewhere to the WEST (left) of True North, these areas have WEST declination."

Now, from the manual of my Silva Ranger compass model 515

"Turn the dial to increase or decrease that reading according to the declination. Easterly,
decrease the dial reading and westerly, increase the reading.
For example, if your bearing from the map is l00º and the declination is 10º East,
DECREASE the reading 10º by turning the dial to 90º. If the declination is 10º West,
INCREASE the reading of l00º to read 110º."

Now, on page 96 of Freedom from the hills, there are two illustrations (figure 5-10 and figure 5-11) If you have this book, you can turn and see what I mean. in f. 5-10, it shows that in Vermont (b) the needle points West of true north, just like the book says, but in Figure 5-11 (B), the compass diagram shows that the declination arrow is decreased from true north to give a reading of 345 degrees North.

Now remember form before that from my compass instructions I am to Increase when I have a Westerly declination? Shouldn't the true declination be set to 15 degrees North, NE? By subtracting, I would be increasing the distance that magnetic north differed from true north, rather than correcting the error.

Does anyone see my point. Am I wrong? If I am, what am I missing? Is N.H. true north 343 degrees or 17 degrees? Thanks if you can make heads or tails of this and sorry for such a long post.

If anything, the map I hold in my hand must be wrong if I am wrong, since it says that NH has a 17degree West declination. Meaning that, the offset between true and magnetic North is 17 degrees West. If the rhyme West is Best and East is least holds true, then I would ADD 17 degrees to my bearing or azimuth.

http://www.atlasquest.com/tutorials/...clination.html

Now, according to this site, there are two ways and one talks of converting true north to magnetic north and the other is the opposite when converting magnetic north to true north. According to that site, the above references from both Freedom of the Hills and my instruction manual would suggest that they are instructing me to convert True North to Magnetic North. It is all so very confusing as I am reading inconsistencies in those two books and then even in a "map and compass" manual written by Cliff Jacobson. If anyone here has that book I can point out the pages I am referring to.

Thanks,

KDT

 

[bikehikeskifish]

If true north is 0 degrees then magnetic north is 17 degrees west, if that is the declination, of 0 degrees, or 343 degrees.

Tim

 

[Rick]

My FOTH Book is an older version and the figures/pages don't tie out.


So think of your compass dial and draw a figure with 2 points one above directly above you labeled "360" and one at 11:00 position and label is "343".

Now take your compass and point it straight at the 360 spot and rotate your bezel until the 360 spot arrives at the 343 spot. You have just adjusted for westerly declination by adding/increasing by (Look at the number that is pointing to 360 position) 17 degrees.

I think the confusion comes in because people think in terms of 343 is less than 360, so subtraction seems to be in order because mentally you are turning the bezel counter clockwise. (I hope I answered this)

 

[Kevin Judy and Emma]

Thanks!

I think he figured it out himself, but this explanation seems more clear than what he came up with.

KDT

 

[jniehof]

I think the key confusion is that moving from map to field you do the opposite of moving from field to map--it's add in one direction, subtract in the other.

I just use a compass with settable declination and forget about it. Drawing orienting lines on the map is another approach (I wish the AMC maps had them.)

 

[Stan]

I never set the declination ... if it gets unset without me realizing it it could throw me off. I always use the math and if I get confused ... ... I remember that, in the Northeast, magnetic north is to the west (left) of true north.

Everytime I stop to think about it, however, I'm reminded of the millipede that froze in its tracks when asked how it walked.

Not to take anything away from the convenience of GPS, I much prefer map and compass, especially in the Northeast where there are so many navigational clues that the technology actually detracts from my affinity with and appreciation of the surroundings.

 

[Dr. Dasypodidae]

I never set the declination ... if it gets unset without me realizing it it could throw me off. I always use the math and if I get confused ... ... I remember that, in the Northeast, magnetic north is to the west (left) of true north.

Everytime I stop to think about it, however, I'm reminded of the millipede that froze in its tracks when asked how it walked.

Not to take anything away from the convenience of GPS, I much prefer map and compass, especially in the Northeast where there are so many navigational clues that the technology actually detracts from my affinity with and appreciation of the surroundings.

I also never set declination, unless I am mapping something geologic. Instead, I tape a list of magnetic bearings for all the key bailout points for a particular trip on the back of my compass so that I never need to think about anything, especially if I should get cold and wet, or hypothermic.

 

[Rick]

I also never set declination, unless I am mapping something geologic. Instead, I tape a list of magnetic bearings for all the key bailout points for a particular trip on the back of my compass so that I never need to think about anything, especially if I should get cold and wet, or hypothermic.

Bingo!!!!

 

[Neil]

I never use a compass with "adjustable" declination because I would have to unlearn previous learning.

What I do like for off-trail navigation is drawing magnetic grid lines on my map. It's basically the reciprocal procedure to adjusting the compass. I learned it from the internet!

Scroll down to this heading near the end of the article:

Map Magnetic Meridian Reference Method.

Here's the -LINK-.

 

[DougPaul]

I never use a compass with "adjustable" declination because I would have to unlearn previous learning.

Its pretty easy--you just set the local declination on the compass and then use the compass and map as if the declination was 0 deg.

Doug

 

[prino]

These are the reasons I like orienteering maps... they are all drawn to Magnetic North!

 

[DougPaul]

These are the reasons I like orienteering maps... they are all drawn to Magnetic North!

And as the pole moves, you will need to update your maps...

Nautical charts are marked in lat&lon (referenced to true N), but have a compass rose to directly get magnetic headings. (Compasses on boats have no declination adjustments.) However, parallel rulers are a bit hard to use on the trail...

On land, I prefer to set the declination on my compass and navigate with respect to true N. (Less chance of making an error in the math.)

Whatever... It doesn't matter which system you use as long as you use it correctly. (And if you have to give a bearing to someone else, make sure you specify magnetic or true.)

Doug

 

[Fitz]

Pole is Moving

Its pretty easy--you just set the local declination on the compass and then use the compass and map as if the declination was 0 deg.

EXACTLY - there's your answer. That is why it is adjustable to begin with.

Just an FYI. The magnetic pole is Wandering. So if you pull your 17 degrees or some other value off a 1932 topo map for example, you may be introducing error.

Here is a website that will give you current declination for a location or zip code.

http://www.ngdc.noaa.gov/geomagmodels/struts/calcDeclination

North Conway today is 15 degrees 44 mins.

 

[bikehikeskifish]

Raise your hand if you can follow a hand-held plastic compass with a 1.5" dial to the minute accuracy. Raise you hand if you can follow it to less than 2.5 degrees. Without using handrails!

Tim

 

[Fitz]

Flipped

Okay, just don't blame me if the pole reverses overnight .

(It is a resource I thought people might be interested in. You don't have to use it.)

 

[bikehikeskifish]

"Measure with a micrometer. Mark with chalk. Cut with an ax. Hammer to fit. Paint to match."



Tim

 

[Stan]

Who needs a compass anyway??? at least on sunny days. If the sun is shining point the hour hand towards the sun and noon will be the direction of south... while 6 is direction towards north. Close enough for most Northeast navigation challenges if you incorporate elevations and topography in fixing your location and direction of travel.

... yeah, always carry a compass. Two is good practice.

Do others feel inspired by explorers who navigated un-mapped regions with none of the technologies we have?

 

[Nessmuk]

Who needs a compass anyway??? at least on sunny days. If the sun is shining point the hour hand towards the sun and noon will be the direction of south... while 6 is direction towards north.

Huh? So if I face the rising sun at around 6:00 or thereabouts, then south is directly behind me? I think you meant to say - "half way between the hour hand and 12 is approximately south".

if you incorporate elevations and topography in fixing your location and direction of travel.

Always use all "clues" available - the compass assists in terrain identification. Then navigation by terrain association with your map is easy.

... yeah, always carry a compass. Two is good practice.

Especially if you use your watch method.
I was once told that an experienced woodsman carries 3 compasses... one as primary, one in case the primary is lost or broken, and a third to give to another poor sole who doesn't have one.