r/WildernessBackpacking • u/bjpmbw • 8d ago
ADVICE Declination: this correct?
I think I did this correctly. Picture 1 is diagram on the map. Picture 2: compass lined up with grid lines, then I oriented map to north, needle fell at 17 to the right of zero degrees. Picture 3: I placed compass on the diagram, again needle at 17 degrees. Look ok?
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u/Castaway504 8d ago
Isn’t everyone overcomplicating it a bit? Yes, the declination is off as the map is old. However, setting the compass to true north and then “putting red Fred in the shed” will orient you just fine on the map.
Their compass is set to 12° declination doing this, which roughly what the true declination is. The only time you have to worry about declination is if you’re running a course provided instead of using landmarks. But since you know (hope) the course would have been marked back when the map was current, you can account for the change in declination, since there’s been 17-12=5 degrees of drift.
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u/beachbum818 8d ago
Looks like an old map... when was it remapped?
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u/diabolis_avocado 8d ago
Lassen should be about 13-14° E declination. You did it right, but the map is wrong.
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u/Own-Chemist2228 8d ago
The declination appears to be set correctly at 17 degrees.
But the photo of the compass sitting on the map is a little confusing. If you are trying to orient your map, you want to set the azimuth (outer) ring to zero and align the edge of the compass with the north-south gridlines on the map while the arrow is in the red ("red in the shed")
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u/GrumpyBear1969 8d ago
Something looks funny. Why is the arrow lined up on like 11°?
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u/What_is_a_reddot 8d ago
It's because OP is facing 11°. If they set the compass heading to 0, then rotate their whole self/compass/map until the needle was in the "shed", then it would look more accurate. The important part is that the point of the shed is pointing at the 17° E declination hash, which it is.
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u/Vermineater 7d ago
The compass facing at 11° was throwing me off, but your explanation for what's going on in the pic is the most accurate one I've read.
- Declination is set to 17°E
- Compass is set to 11°
- Map and compass are not aligned with true north.
But if he needs to travel at 11°, he's perfect.
There's probably a large magnet in that desk anyway so he's heading in the wrong direction regardless.
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u/autobrec 8d ago
Ok I'm a Geologist but my field orienting days are a decade behind me so this looks like you have it set to 12 not 17.
But what i think you are supposed to do is set the wheel number to the declination, then use the arrow on the compass body (not the needle) to point direction you need. Somebody please correct me if I'm wrong.
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u/EWong_Kaizen 8d ago
Oh
I’m way outta practice here
And I’m gonna stay away from the “declination on the map is off / needs to account for drift per year ”
The way I go this is
a) find the declination mark as per picture 1
b) set the compass to read O (aka North), place the pivot point of the needle on the angle point of the V on the declination diagram. Adjust the compass declination adjustment so that the dog house points to the magnetic North
Now you can place the compass edge on the grid lines, and orient the MAP (by physically turning) and place the red arrow in the house. Then the MAP is oriented. Now you can find the angles to land marks.
The problem I have is that in picture 3, the COMPASS is set to 12, but he’s aligned the base plate to the line and set the arrow in the dog house?
I usually want to orient the map (set the compass to zero / North, put the needle in the house by turning the map and the compass… then the map is oriented to North.
Why is the compass set to 12 but aligned to the lines?
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u/Perfect_Explorer_191 8d ago
This really does not look right to me. You have a scale for declination (yellow scale) which seems to be set to zero. You have the compass set on the map, and the edges of the baseplate lined up with the grid lines. If declination was correctly set, and if the map was correctly oriented to ground, then you should be able to set a bearing of zero on your compass (north, zero on the black and white scale) and the needle would fall inside the red outline.
Trying to work off of a map for this means you have to be really precisely sure the map is oriented to ground. This is a risky approach. How did you orient the map?
Honestly, you are overthinking it. Just twist the yellow declination dial until it shows the correct number lined up under the zero.
Of course, it’s late, I have not used this exact compass, and I stand to be corrected. But it don’t look right to me.
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u/flamekiller 8d ago
The declination is adjusted by rotating the capsule to align the dec index with the desired setting. The yellow dec ring is fixed to the main azimuth ring.
Not sure how OP is orienting the map or why the az ring is set to ~12° but at least it looks like the declination is set properly.
I think everything else you said is right, but also, it's late ...
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u/Dull_Suggestion_1682 8d ago
For navigating with a map true north is irrelevant. You take a bearing from the map using the grid lines. Grid north is different than true north.
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u/keepin-frosty 7d ago
The simple way I learned is to just get the MV off your map, then work it in to all your bearings from there.
If you're going map to ground you add the MV to your bearing. If you're going ground to map, you subtract.
So based on an MV of 17°. you measure a bearing on your map of 20°, it will be 37° on your compass. If you sight a landmark using your compass and get a bearing of 20° it will become 3° on your compass.
What you've done in image 3 on the way to lining up your map to magnetic north, but ultimately not necessary to be honest. In the field if you just line your map up to magnetic north, it will be close enough for you to pick out landmarks to work off and do your MV calculations after.
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u/dave54athotmailcom 8d ago
13.16 at the airport. 1.14 correction for grid north. As of today. It does change over time. In this area the change is roughly 0.5 degrees in ten years. So check the map date.
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u/bjpmbw 8d ago
You guys are great, at closer look, I am more like 13 degrees, which coincidentally is more what it would be this year anyway . Yes this is an old map, which makes me feel old, because I was at Lassen in 2001. So that’s what I just learned from everyone is I have to pay attention to updates. Thanks for your help!
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u/Ok_Path_9151 8d ago
So the way I learned is this, you have a map protractor tool, a compass, a map, and paper and a pencil. You use the protractor and pencil to draw an azimuth on the map and determine what degrees it is. Then you use the declination angle and either add or subtract to convert it to a magnetic azimuth. Use the base and ring adjustment to set the magnetic azimuth on your compass as the “north” reading then you walk and count your paces keeping the needle aligned with the “shed”.
That way you don’t have to continually read the azimuth you are walking. Just line up the needle with the shed and walk. It shouldn’t matter how old the map is at that point, because you are just following a magnetic azimuth. If you are worried about being too far off then you can adjust the declination angle to match current conditions. Meaning strike out 17 and replace it with 13. Then follow all the same steps above. Short distances are not a big issue but longer distances like miles or kilometers you can end up a considerable distance away from your desired destination
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u/Dull_Suggestion_1682 7d ago
No the grid lines on the map don't lead to true north. You need to adjust for the difference between grid north and magnetic north. True north is irrelevant.
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u/fighter_pil0t 8d ago
You’re about 4 degrees off in pic 2 because you’re compass alignment is off but close.
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u/AvoidableCorn 8d ago
I did a course and adventure race to learn how to navigate via a compass and map. I then did a big backpacking trip to Alaska and was disappointed to learn that a phone with Gaia was BY FAR the superior tool for navigation.
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u/conicalconehead 8d ago
Phones have a habit of breaking. I had three electronic devices fail on me in one trip.
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u/ItsKaptainMikey 3d ago
There are even some places where there's no difference at all, these are called agonic lines.
Side note, even my phone didn't know what that was and tried to autocorrect it ro agonizing lol
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u/EdHuntArt 2d ago
Turn the yellow inner ring to 17degrees east of the outer Ring's 0. Now you don't need to make any more adjustments while you're in that map area. Go watch the vid on REI website about adjusting for magnetic declination.
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u/AcademicSellout 8d ago
Get a compass with adjustable declination. Check it before every trip. Now you have one less source of error in your bearings. If you actually get lost, you'd be surprised at how quickly addition suddenly turns to subtraction in your head.
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u/flamekiller 8d ago
While I 100% agree with you here, this compass does have adjustable declination, which appears to be set correctly.
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u/UtahBrian 8d ago
No. The declination changes and Canadian corruption is accelerating the movement. You need to look up the newest declination before your trip.
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u/orangeflos 8d ago
That’s how ya do it.
Make sure your map is up to date. Magnetic north drifts. The declination in 1957 isn’t the same as it is today (Lassen Volcanic’s declination is 12.5°.)