Declination and compass configuration

[darsenator]

Hello...

I have a query regarding "How to adjust my compass for declination".
I'll be doing some walking in Bunyip,VIC and as per several websites am aware of the following information.

"Magnetic Declination is the angle between True North and Magnetic North (which is always east (positive) of True North in Victoria)"

The topo~ map I have tells me that the declination is 11 degrees.

My query is, when setting the dial in the compass, does this simply mean that I move it east (right) so the magnetic needle is orienting arrow 'N' is set at "11 Degrees East" ?

I'm just starting to learn about navigation and using compasses so some things are unclear.

Thanks for taking the time to read my post.

[Gusto]

In Victoria you subtract when converting from Map to land. The reverse applies when going from land to map.

This forum thread has lots of information about it.

http://bushwalk.com/forum/viewtopic.php?f=5&t=9023

[andrewp]

When using a map to take a bearing it is actually the angle between grid north and magnetic north that is important. This is known as the Grid Mag Angle. Magnetic Declination refers to the angle between true north and magnetic north. In Victoria the Magnetic Declination it is between about 10 and 13 degrees east, but in Perth it is 3 degrees west and in NZ it is ~25 degrees east. Some maps show the relationship between true north, grid north and magnetic north, other just show grid north and magnetic north.

Here is a link to the Map Reading Guide produced by Geoscience Australia and it is well worth a look for an understanding of navigation and map reading principals.
https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&catno=63639

[darsenator]

Hi Guys,

Thanks a lot for replying to my thread...

I checked out the links provided and it's starting to make more sense.

So if I'm in Victoria would the compass magnetic needle need to be set as per the picture below if the declination is 11 degrees



regards,

Darsenator

[darsenator]

Do I have the right interpretation below ?

As per the diagram

The declination Vic,Australia is east , this means that the compass orienting arrow/magnetic needle need to be aligned to correct declination angle pointing east by recommended degrees




and when in Western Australia the compass orienting arrow/magnetic needle need to be aligned to correct declination angle pointing 'West' by recommended degrees

Is this right ?

[Gusto]

I think you're on the right track, but you've caught the wrong train.

Previously I mentioned that "In Victoria you subtract when converting from Map to land. The reverse applies when going from land to map. ".

What I failed to state was how you do that. The short description is that you add or subtract by rotating the Bezel in relation to the base plate of the compass.

Your photo implies that you have rotated the entire compass in relation to Magentic north. Technically speaking it would be possible to alter your bearing using this method. But you would need to be good at what you're doing as you're increasing the difficulty.


On a side note, you should be rotating the Bezel anyway when bearing, backbearing and triangulating etc.

[darsenator]

Hi Gusto,

I'm obviously having trouble getting my head around this 'declination stuff'.
I watched a "Youtube video" in which the presenter advised that 'declination' is only important for orienting a map, would you agree ?

I'm aware that some compass's allow the declination to be set using a screw underneath the base , would one of these make it easier rather then having to remember to add/substract ?

[Gusto]

Rotating the map by the difference in declination when orientating the map is a reasonable action to make. It would only be of use if you were stopped and were able to see land marks that are long distances away, this is a common situation in the Alps.

However rotating isn't practical or accurate if your on the move. It's also a rather useless if you can't see far away, eg surrounded by trees/land etc. Also the scale of a map would rarely be able to accurately be able to represent all the twists and turns on a track as well. So if you can only see a small section of the track then rotating the map is still irrelevant

Sorry, I'm not explaining this very well, I don't have the time right now.

[Gusto]

http://www.youtube.com/watch?v=0XMirGx1nwc In this video everything is explained about taking a bearing, except adjusting for declination. You'll note he doesn't rotate the map once. Because rotating the map is irrelevant for some things. In that video he goes from a map bearing to then pretending to walk on a bearing. It is between these to process that you adjust for declination.

I haven't the time to watch this one, but presumably this one covers it. http://www.youtube.com/watch?v=-N8roXXgIhM

[darsenator]

Thanks a lot Gusto,


I'm checking it out right now...really appreciate the time you've taken to help me understand this, it''s certainly given me some different angles to the approach of learning.

best regards

[darsenator]

Hi Gusto,

I'll have another crack at this .... ( I can't believe I'm having so much trouble with this..)

Below are the declination details of the map I'm using


Below is the front cover of the exact map I'm following


So if the declination for this map is 11 Degrees East, does that mean that if the bearing for a given point to which I want to get to on the map is for example (40 Degrees east) that I need to really travel 29 Degrees East (because I have to subtract when in East) ?


"In Victoria you subtract when converting from Map to land. The reverse applies when going from land to map.

[darsenator]

I'm thinking of buying a compass like the Sylva 515 which has the "Permanent Declination Feature"....

[Rob A]

Fairly concise from your vic gov maps. There are all sorts of mnemonics for people to get flustered over. Just think about what you "actually" have, a compass that has a head start.

[Gusto]

Hi Gusto,

So if the declination for this map is 11 Degrees East, does that mean that if the bearing for a given point to which I want to get to on the map is for example (40 Degrees east) that I need to really travel 29 Degrees East (because I have to subtract when in East) ?

Correct 40 degrees as a map bearing becomes 29 degrees when using the compass on land. And so applying some logical thought.. a 29 degree bearing from the land become 40 degrees on the map.


That map is also up to date as of 2010. That's very new. It's worth noting that over time declination changes slightly over time. So a map dated from the 70's can be a couple more degrees out than what it actually states.

Cheers

[darsenator]

Ok, cool ...I think I'm getting it....

If I buy a compass with the adjustable declination scale, would that mean that I don't have to worry about subtracting/adding as the compass will always point to "True North" {assuming I've set the correct declination as per the map} on the compass ?

I refer to the following wiki.

[Gusto]

I've never used a compass that can be set for a specific declination. I've taught lots of students how to use compasses. It seems to me like an extra feature to pay for and an extra complication to the device.

The main issue people seem to have is that they get to hung up on trying to be dead accurate as to if its 10.5 or 11 or 12 or 12.5 or 13 degrees etc. This creates a bit of angst, that they may get it wrong. The reality is, just using a declination of between 10 - 13 degrees is fine.

Navigation is never actually about being exactly perfect. It's about being making every reasonable effort to be accurate and acknowledging that a degree of error is always going to occur.

Gaining a grasp on what the land should look like based on what the map is telling you is the other key component. You'll be most accurate If you can do this reasonably well in conjunction with using the compass reasonably well.

Cross checking what you can see and what you can remember seeing. Then making predictions of what you are expecting to pass by in the future.

[photohiker]

If I buy a compass with the adjustable declination scale, would that mean that I don't have to worry about subtracting/adding as the compass will always point to "True North" {assuming I've set the correct declination as per the map} on the compass ?

Yes. If the Declination is set correctly, then you can work your navigation as if there were no declination.

Best thing to do is to get out and practice in a safe environment.

[darsenator]

Well....Thank you to all the forum members who have taken the time to reply (Gusto,Rob A,Photohiker,AndrewP)....

I now have a really good understanding, and everyone's point-of-view has being great...

Best regards to all.

[taswegian]

Just a warning about compass with separate declination setting.
That is fine IF you ensure it hasn't changed (the setting , not the local declination) each time you use it.
You could end up just assuming its right and off you go 12/13°out.

Also as Gusto indicates, for course navigation a few degrees either way doesn't necessarily mean you will miss your mark.
1° subtends about 17.4 metres at 1km.
Unless you are running very accurate lines then accuracy is somewhat relative.
And then you would not be using a compass such as illustrated.

Don't confuse super accuracy in theory with reality on the ground.
If you can grasp what Grid north and Magnetic north mean then the rest should follow.

[Strider]

Wow so much complication. Is the question not just whether to rotate the bezel left or right to allow for an Easterly declination?

[photohiker]

Just a warning about compass with separate declination setting.
That is fine IF you ensure it hasn't changed (the setting , not the local declination) each time you use it.
You could end up just assuming its right and off you go 12/13°out.

This is a good point. I have seen one or two compasses that have a pretty loose declination adjustment and it is conceivable that they might get nudged out of adjustment in use. On the other hand, most are reasonably stiff, the best being the Suunto which come with a tethered tool on the lanyard which is required to make the adjustment. (it's a screw type adjustment, my Silva is a friction adjustment).

Once you have familiarised yourself with the compass and declination adjustment, you do notice while using the compass that the declination has been adjusted, so I don't want to give the impression this is a deal breaker for in-compass declination adjustment, unless the adjustment is very sloppy. Check before you buy!

On that note, if I were buying a compass today, I would probably get a Suunto M3 Global. I found a useful user review of the M3 Global here.

[Rob A]

Still this but;

" .... FLAWS .... 2. It has developed a bubble in the compass housing, which if like in our Silva compasses.... "

Bit of a nuisance if you fly with the thing occasionally. The pressure changes do seem to exacerbate the problem.
Do they all come out of the same factory and get branded, or use common stocked parts?

[photohiker]

No idea Rob. I've flown with my compasses a fair bit and never had a bubble.

I carry them in hand luggage though, so maybe that's not the same as carrying it to the top of Mont Blanc in winter or leaving it in the hold.

[Rob A]

Holds will still be pressurised. But the bubble in my silva seemed to grow with travelling by air. Once the bubble got bigger, the problem seemed to accelerate. No longer functioned and been binned now. Will grab a Suunto next time I see one.

[Gusto]

Wow so much complication. Is the question not just whether to rotate the bezel left or right to allow for an Easterly declination?

+1 - I wasn't very concise.

However it's not clear how darensnator actually knew about compasses in general. And It would appear as though he was watching a YouTube video that suggested using techniques that I don't wouldn't promote.




As for navigation, it's worth understanding that the most guaranteed line to take through the bush is often the fastest route. But NOT the shortest. People will intentionally choose a route that is longer in km if it ensures that they know where they are going and have less risk of making a mistake.

[darsenator]

Hi Gusto,

You're right....new to the "Navigation scene" so it's a learning curve for me at the moment....

Great to bounce of other peoples knowledge,experience and guidance.

Got all confusing whilst you-tubing, so I'm glad I came across this forum

Many thanks and regards.

[neilmny]

If I buy a compass with the adjustable declination scale, would that mean that I don't have to worry about subtracting/adding as the compass will always point to "True North" {assuming I've set the correct declination as per the map} on the compass ?

Yes. If the Declination is set correctly, then you can work your navigation as if there were no declination.

Best thing to do is to get out and practice in a safe environment.

This is also how I prefer to use my compass.
The safe location in the field practice is a key factor to making it all come together and make sense.
It only takes a moment to check that the declination is still set correctly each time I take it out for a trip (just like my other gear gets checked).
Setting declination requires the turning of a small screw inmbedded in the bezel and it would be quite difficult to knock the alignment accidently anyway.
The compass also has a "inclinometer" although the last thing I think of when trudging fully loaded a up a "cliff" of a hill is how steep the angle is!
My compass is the Silva Expedition Compass and I bought it here http://www.forestrytools.com.au/index.php?id=21 (no affiliations)
The scales and declination trim gave me what I wanted for what I think is a fair price.

[photohiker]

Will grab a Suunto next time I see one.

Easier said than done. I haven't seen many, and definitely not the M3 Global which is what I'd buy if I saw one. My UK Compass does not have declination adjustment, so I might pick a Global M3 up from the UK. Plenty in the US, but they come with Mile scales and 1:24000/1:62500 on the bezel. There are some on ebay (inclinometer missing, but the correct map scales) and I have seen some in UK online hike stores, eg: hitchnhike.co.uk. UK pricing seems to be the most reasonable, be even better if the store rebates the VAT 20% which would probably cover much of the freight.

neilmny, does your Silva Explorer have a global needle? Other wise it looks to be very similar to the M3

[neilmny]

No it's a local needle. I accidently bought (ie. didn't have a clue) a northern hemisphere compass on ebay so made sure I atleast got a local (southern hemisphere)
version to replace it. It's interesting that you can get a global needle......I wonder how that works?

[photohiker]

It's interesting that you can get a global needle......I wonder how that works?

The needle is not the magnet. It's all a tricky jewelled gimbal setup: http://en.wikipedia.org/wiki/Suunto#Glo ... dle_System



That's the MC2-G compass, the only other Suunto with global needle. It's basically the sighting version of the M3 Baseplate compass. JerkingTheTrigger Review of the MC2G