View Full Version : Declination anyone?

09-26-2008, 06:26 PM
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.

09-26-2008, 06:52 PM
You are absolutely wrong. No idea which part is wrong. But there must be a part that is wrong. Always is.

That being said, I am not a good compass-ist and am not normally inclined to decline my compass readings.

Is it possible one explanation is saying to adjust the compass by increasing the heading (in degrees) and the other is to adjust the heading the other way to compensate?

09-26-2008, 07:24 PM
I don't think that is what the two explanations are saying. Bearing is actually a nautical term and we usually use it when we should be saying azimuth. A nautical and land compass are different in how the degrees are scribed. The nautical bearing compass is divided into 4 90 degree segments, and the other 360 degrees. Now, that being said, I am not an expert with a compass, nor am I an amateur.

It really would be helpful for anyone who has a copy of "The freedom for the hills" mountaineering book to give me some assistance, though I do thank you Brad for your opinion. The compass is always correct (unless broken), but in this case I have my doubts that I am "absolutely wrong" as you put it. If you wouldn't mind clarifying how you think I am wrong without fully understanding the "how" I would be grateful. 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.


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.

09-26-2008, 09:31 PM
Alright, please excuse the double post, but I think I have it clarified and figured out now. A while back I had asked someone if after having set the "fixed" declination adjustment, should I use the declination arrow as the orienting line which I would align with the map's meridian lines. That someone said yes, which threw me off. That was wrong advice and I got it straightened out. This link helped me the most and perhaps it will help anyone else out there who was wondering about declination.


So, I was half right and half wrong in my understanding of what "Freedom of the Hills" described. I do add for a westerly declination, but only when using the temporary method for adjusting for declination, otherwise I just keep my bearing and adjust my needle to the doghouse after I have made my adjustment with the gear plate.

Bill O
09-27-2008, 08:40 AM
Sorry, I've never sat down and worked through declination.

I'm a GPS man. I encourage everyone to know how to use a compass, but GPS changes everything.

09-27-2008, 09:25 AM
yeah, I don't have the money to replace my Garmin etrex GPS (it mysteriously quit working last summer) since I am saving every penny for both my winter trip to NH and my trip this summer to Alaska. I don't think I will have to worry much about declination up in NH since we will only be around Mt. Washington, but I wanted to figure it out for myself and I think I have finally made some headway.

KD Talbot
09-27-2008, 07:20 PM
I put the question out on another forum and got this explanation:

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)


09-27-2008, 09:30 PM
yeah, thanks KD, that is indeed a good way if your compass does not have a built in declination adjustment dial.

09-29-2008, 09:37 AM
I am coming in late to this post but the quickest simplest way to answer this is to take out the map that you will be using with the compass and it will tell you what you need to add or subtract depending on the where you are at. It is hard to understand what the book says as I can't see the pictures. I would consider myself pretty good when it comes to compasses but it has been a view years since I taught any one how to read one and doing so over the computer may be a little hard. If you are still having problems you might want to go to a local store IE: REI or EMS and ask some one to show you. It is certainly a lot easier with a map, compass and protractor in front of you to explain it. Good luck

09-29-2008, 09:45 AM
Thanks, but I have it figured out now. I am glad I learned this way, since I now possess a myriad of examples to teach other people. It is a bit more than just reading the map and adding or subtracting if you don't understand the whole concept of declination. As in Westerly declination you are indeed moving your declination indicator (if your compass is equipped with one) in a minus 0 degree position, but what you are really doing is adding that declination to make up for the magnetic error. Hence the phrase "East is least, and West is best". Books are good for information, but with some things you do need to go out and actually practice it for it to really sink in.