compass declination question

B

bill_G

Joined
Jun 7, 2004
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bought a compass. first one in 25yrs.:) you can set the declination on it.

its a suunto m3. i live in central PA, which is -11 degrees declination.

do i set the underlying bearing arrow 11 degrees to the LEFT or RIGHT of "N"??

after reading some on the web, i think it should be to the left of "N" (north) on the dial.....correct?

thanks........Bill
 
That's right, if your declination is 11 west you want the gate to run 11 degrees to the 'left' of the N-S lines as you look at the compass.
 
Instead of messing with declination, orient your map using your magnetic north line instead of true north. If you forget to reset your declination, you'll be way off course.
 
k_estela said:
Instead of messing with declination, orient your map using your magnetic north line instead of true north. If you forget to reset your declination, you'll be way off course.
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Be careful doing that. The only line I know of on a USGS 7.5' that even attempts to represent mag north is the line in the declination diagram, and it's just a relative representation, not truly accurate to mag north. If bill_g wants to use the compass to walk an azimuth he has pulled from the map, he'll need to account for declination, especially 11° of it.
 
mapper66 said:
Be careful doing that. The only line I know of on a USGS 7.5' that even attempts to represent mag north is the line in the declination diagram, and it's just a relative representation, not truly accurate to mag north. If bill_g wants to use the compass to walk an azimuth he has pulled from the map, he'll need to account for declination, especially 11° of it.
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You can always take a protractor and draw a correct declination line on the map. I always check the declination diagram to make sure it is correct.
Oldman/Marty
 
There are places where the declination is much more than +or- 11 degrees , most if not all topos are orientated to true north to the top of the map orientating the map to compass envolves getting the map orientated to true north after ajusting the declination of the compass.
 
I also just bought my first real compass (Recta DS 40) and taught myself how to use it. Luckily, in central europe declination isn't important, because magnetic north and geographic north are almost identical.
But if I travel somewhere, where declination matters, what is the way to go with a compass that has a fixed declination scale?
I'd say the easiest and safest way is to draw magnetic north lines on the map, so that map and compass always "speak the same language". Am I right or would you do it differently?
 
DocArnie said:
I also just bought my first real compass (Recta DS 40) and taught myself how to use it. Luckily, in central europe declination isn't important, because magnetic north and geographic north are almost identical.
But if I travel somewhere, where declination matters, what is the way to go with a compass that has a fixed declination scale?
I'd say the easiest and safest way is to draw magnetic north lines on the map, so that map and compass always "speak the same language". Am I right or would you do it differently?
Click to expand...

Personally, I'd get a compass that I can adjust for declination. You can draw mag north lines on the map, I have done it as an exercise, but found it to be quite a hassle, and declination does change over time. I've been using a map and compass for 20 or so years, and understand the 'theory' behind declination and can puzzle out how I need to adjust for it if I have a compass that cannot do decl adjustments, but when I'm tired and been in the field for a week I'm not sure I won't make a mistake, even after 20 years.
 
+1 for the compass with adjustable declination. The Suunto M-3 is probably the best deal in a baseplate compass out there right now. Nice quality and features.

But ... I also agree that orienting the map to north is a good practice.

The way I remember which direction the needle tends toward - at least in the continental US - is I picture that it wants to point toward the Mississippi river valley, which is roughly where the zero declination line is. If facing true north, west of the Mississippi the needle points right of N. East of the Mississippi the needle points left of N.
 
I often find myself working in in areas where the magnetic declination is up to 30 or 40 degrees, so for me it is very important to use a compass with adjustable declination (I prefer the Suunto MC2 International), working on a magnetic grid is not even an option in these areas.

One thing related to this and something I find myself always having to remind people about, is that grid north and true north are only equal on UTM sheets at the equator and can vary by up to 3 degrees in the polar regions, so don't forget to take this into account if navigating with your GPS set to "true north", this may be accounted for by adding/subtracting it from the declination value when setting your compass so that your GPS bearings/tracking is in agreement with your compass and map.

Here is a declination map for those of you not familiar with it:

http://www.ngdc.noaa.gov/seg/WMM/data/wmm-D05.pdf

Note that in areas where the field lines are close together, such as the central and eastern Arctic in Canada, the declination can vary even across a single map sheet, one must be aware of this change across the sheet. The value listed in the legend of a UTM map sheet is for the centre of the sheet.

(a tip: rather than calculate the declination from data on your map sheet legend for your current date use the "automag" function on your Garmin GPS to get the current calculated declination for your location).
 
This declination stuff has got to be the most confusing stuff ever created.
map to grid...ehhhh, subtract? If it's a negative declination you...add?? Depends, right? Unless you're in the Western states? BHAAAAAA!!!
I remember some type of rhyme to remember it, but that just confuses me even more.:confused::grumpy:
 
I wish somebody could finally explain this stuff to me so I can understand it without the use of rhymes or anything. I've used this stuff back when I was in the Army....most of the time I think I just lucked out when it came to Land Nav.:)
 
Add East Correcting.

True Virgins Make Dull Companions =
True - Variation-Magnetic-Declination-Compass

What these to mean is that if you are taking a compass reading and want to get the true bearing; you add your declination if it is listed as E, subtract if it is W. Variation will probably only come into play onboard ships or maybe inside an iron ore mine.

BTW: For a more PC version you can reverse the order and get the new memory aid of:

Can Dead Men Vote Twice.

Last but not Least: ADD EAST CORRECTING
 
Can you do the Magnetic to Grid thing, or are you already doing it?
Thanks....I've got some major mental blocks to understanding this stuff due to Uncle Sam's teaching method.:)
 
O.K., so if I'm going from compass to map, with an Eastern Declination, I add the declination amount, right? So, if I want to go from map to compass, I subtract, right?
From the rhyme (or whatever it is) "Add East Correcting", how do you remember which way that you want to go in order to use it? (map to compass or compass to map?):confused:
 
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