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Old April 25, 2013, 07:31 PM   #1
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Always trust your compass? Right? Wrong!

Was tramping up a river bed with my son in a remote part of New Zealand last week when we came across a lot of rusty looking rocks. Speculating that they might contain iron I tested one with my compass - not a flicker. But then I thought "Crud! No way is North that way. Must be a big anomaly around here."

So my son pulled out his identical compass and this is what we found

Seems as if the polarity of mine had been reversed. Apparently this can happen if a compass is exposed to a strong magnetic field over a period of time, but I can't think where this could have happened. I keep it in the top pocket of my pack which it sometimes shares with GPS, binos, camera, rangefinder and topo map.

Thought I would mention it on the forum as something to be aware of as it could really throw you if relying on a compass in thick bush or in fog such as below.

I think I will make it a practice on future trips to always check my compass when I set out. In practice we don't use compasses a lot as navigation is pretty simple in this mountainous terrain though finding a safe route can be problematic.

I believe you can reset the polarity by stroking with a strong magnet. Anyone tried this?


Last edited by Brian Pfleuger; April 28, 2013 at 08:24 AM.
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Old April 25, 2013, 07:57 PM   #2
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I have read about this problem but have never experienced it. I now carry a second compass (different brand but similar design) and I keep them as separated as possible. I have not had to reset polarity, but have read that it works. I like Silva, Suunto and Brunton.

Also: I would love to hunt in New Zealand but doubt if I will ever be able to afford it. I spent a week in Sidney, Australia about 43 years ago (a brief "vacation" during my tour of duty in Vietnam.)
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Last edited by lefteye; April 25, 2013 at 08:09 PM.
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Old April 25, 2013, 08:49 PM   #3
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Sound like the GPS might be a problem...

never had a "Silva" go bad like that.

I have observed other hunter come up to me asking to confirm North and I'll ask why and observe that they are holding their compass right by the firearm.

leave out iver night on wood post and see if it reverses.
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Old April 25, 2013, 09:31 PM   #4
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I believe you can reset the polarity by stroking with a strong magnet. Anyone tried this?
Never done that stroking thing. But if you think it can be done. Why not. After all your compass in its present condition you'd be better off carrying a sextant.

Since your compass only had a 1 year warranty. I would just pitch it and buy another. I've used one of their Fish Eye compass's for a few years now without any problems. But I indeed have seen a compass or two over the years get bounced off the side of trees and left where they landed for future historic discovery.

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Old April 25, 2013, 09:37 PM   #5
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Whats a Compass? I thought GPS obsoleted them.
Just kidding, I keep my Compass in my hunting pack. I keep my GPS in my pocket. I have a surplus Vietnam war U.S. army Compass. I think it could survive being run over by a tank.
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Old April 25, 2013, 09:41 PM   #6
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If you stroke it and get it fixed, will you ever trust it again. I always carry one of those Marbles, pin on ball compasses to check my good compass
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Old April 25, 2013, 10:18 PM   #7
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Apparently a known problem

Did a bit of goggling and found this in the FAQ on the Silva website

My compass no longer points North. Is this normal?

Please be aware that a reverse polarity is caused by exposing your compass to articles with iron content (something as simple as being placed next to a pair of scissors or a knife for a length of time, microwaves, high tension wires, etc.). Your compass can be repaired at no charge. Please contact us in advance for a return authorization number and shipping address. From the U.S.A, call 1-800-572-8822 between 8 am-6 pm, eastern time. From Canada, call 1-800-263-6390
Not a great help to me in NZ so I think I will try stroking mine with a magnet.

Whats a Compass? I thought GPS obsoleted them.
Ah! But a compass does not require batteries
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Old April 26, 2013, 06:37 AM   #8
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I used to be an instructor on the army. Of all the training a did as well as the classes I did the instruction, the map and compass was the most testing.

The military compass isue usauly has a mirror in it. We juked and said it isso that you can see who is lost!
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Old April 26, 2013, 07:28 AM   #9
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One thing that I always thought I could trust was my compass. There have been a couple of times that it came down to believing the compass or believing what every fiber of my being told me was the right direction. I always went with the compass and always got home. Now you've made me nervous.
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Old April 26, 2013, 07:57 AM   #10
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Are you sure it wasn't because it was made in China and someone painted the wrong end red?
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Old April 26, 2013, 08:21 AM   #11
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Don't anyone use a watch to check your compass any more????

Guess that went out with digital watches.
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Old April 26, 2013, 08:26 AM   #12
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Just guessing here, but if you keep it with your GPS, which is an electronic device, with a magnetic field, that may have done it.
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Old April 26, 2013, 08:47 AM   #13
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I have the same compass a few months ago it was sitting on a shelf and I noticed it was wrong.. I thought that is weird, so I showed the wife and she pointed out it was next to a key holder that had a magnet. never knew.
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Old April 26, 2013, 09:59 AM   #14
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Like LT Dan...

I was also a US Army instructor - for 4 years on active duty, plus 8 years in the Army Reserves.

As LT Dan stated, the "Map Reading & Land Navigation" courses (usually 8 hours classroom and a 4 hour practical exercise) was most challenging to teach, and most difficult for students to learn.

Other instructors frequently asked me to take over "Senior Instructor" duties for them, while they served as assistant instructor. Since my branch was Field Artillery, I was accustomed to being sure I knew where the rounds were going to land before initiating firing commands.

That said, I always used 2 compasses, AND a topo map, in conjunction with each other. In teaching students to use a compass, I included the precaution to be aware of magnetic influences, such as the presence of iron objects (rifle, pistol, trucks, railroad tracks, overhead power lines, hand grenades hanging off your web gear, etc.) The army even specified exact "standoff distances" for each object, and included several questions in the end of course test to be sure the students understood/learned that a compass needle is sensitive to magnetic distractions, some of which are not obvious.

As far as iron ore soil/rocks, underfoot, you can't standoff from such being underfoot. That's when your topo map is your best hope. "Don't leave home without it" is a good rule of thumb.

Now I must humble myself a bit.

I was hunting in thick cover in the East Texas Piney Woods, a mile or so from the nearest road, following a creek bed, and decided to walk back to the road on a straight line, using my compass. It was cold enough that I was wearing a pair of mittens over a pair of gloves. The mittens had a feature that allowed you to fold back the part that covered the fingers, thus allowing greater dexterity with the fingers. When folding back the finger covering, a magnet in the finger covering clung to another magnet on the back of the hand.

So, I uncovered my fingers to more easily manipulate the compass, and proceeded to march straight toward the road, stopping every 50 paces to hang a blaze orange piece of surveyors tape on a tree, so I could return later and set up a tree stand. After marking off about 4 such waypoints, I looked at my back trail and noted that I had formed an erratic zigzag with my markers, rather than the straight line I had expected.

First, I checked my 2 compasses against each other, and they were erratic. Then I shot a back azimuth from my location to the next marker.It was wrong, with both compasses. Finally, I carried my rifle (a possible magnetic distraction)10 yards off the trail, then went back to my last marker and measured the back azimuth with both compasses. Every azimuth I measured, both compasses, was erratic.

Searching for other magnetic distractions, I discovered the magnets in my mittens. I took the mittens off, put them with my rifle, 10 yards away, then took azimuth readings. Problem solved! I then went back to my first waypoint, collecting all of my markers, and proceeded to lay out a straight line to the road.

Lesson learned.

The magnetic mittens stayed in the woods! Ten yards off the trail!
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Last edited by Major Dave (retired); April 26, 2013 at 10:06 AM.
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Old April 26, 2013, 10:16 AM   #15
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Which compass?
I have a military lensatic, a watch compass and a mini compass on my watch.
And a GPS.
They might find me nose down in a field some day, but my head will be pointing toward camp.
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Old April 26, 2013, 10:20 AM   #16
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Another comment

While I realize you put the two compasses within an inch or so of each other so we could see the reverse polarity, they should be separated by 5 meters when checking one against another. This is so because each needle is magnetized, and the magnetic field of one will interact with the magnetic field of the other, causing both to be inaccurate, even when the polarity is not reversed.
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Old April 26, 2013, 11:33 AM   #17
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As Kraigwy said, you can find South with an analog watch or you can make a rough sundial if you have a digital. Point the hour hand at the sun and halfway between the hour hand and 12 is relative South.

When I'm out in the great outdoors I tend to depend more on maps and knowing various geographical features. If this is stream X and that is mountain Y then I should be about here.

Here In Washington, if you can see one of the big mountains general directions are a snap. If you start the day with Mt. Adams West of you, it's always going to be West.
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Old April 26, 2013, 02:22 PM   #18
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I can recall a couple of such adventures.One was somewhere in the vicinity of Pagosa Springs,Colorado.I had stayed on my stand late,was traveling in the dark.Must have been magnetic iron in theground somewhere,my compass was totally confused.So was I.I got into a a bunch of little finger ridges with beaver bogs between them.I found myself on a little patch of ground surrounded by beaver pond and bog,no light,and,elk season in Colorado is never swimming weather.

A buddy helped me out of that one..he knew the country,I did not.(Yeah,I know,I did not do everything right.I did stay dry)

Another one had to do with a nice Hawken rifle I built off the Cherry Corners original blueprints taken from Mariano Medina's rifle.

The Sharon barrel was magnetic.It got tiresome setting that rifle down,walking off a ways,then going back to pick it up,but it sure confused a compass.
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Old April 26, 2013, 06:13 PM   #19
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Some useful comments, thanks.

Thanks for the comments and stories, everyone. Had a few chuckles and could relate to some of the incidents.

I agree that the best navigation tool is a topo map in a waterproof bag. I use MemoryMap to print off an A4 sheet of the area I am going to and put it in a ziplock bag. I also print off a second copy which I mark up with our route and intentions and leave with my wife.

I have tested the compass with all the things I carry close to it in my pack. Nothing obviously affected it. Not surprising seeing that Rangefinders etc are mostly plastic or stainless steel which are not magnetic materials. I too suspected the GPS but the compass barely twitched with the GPS whether on or off.

Before taking the photo I did wander around with the compass a bit to see if that made a difference. But nothing. We then pulled out the other one which worked fine.

I haven't "stroked" mine yet as I want to take it along to our next volunteer SAR training session as an example. We use compasses occasionally for such things as maintaining the line of a search or taking cross bearings on the location of a missing person identified by a cry or by light.

Now you've made me nervous
I agree with you 603Country. The main purpose of the post is to make people aware that compasses can reverse polarity and to check them before use. There is one indication that reversal may have occurred which will be apparent in the field. If you place the compass on a flat surface and the needle is tilted badly so that it is touching the card or close to it then polarity reversal may have occurred.

For those who don't know, the reason is that the Earth's magnetic lines of force are not parallel to the surface of the Earth. A compass needle tries to align itself with the lines of force so that in the northern hemisphere the north end of a compass needle will point downward and in the southern hemisphere upwards. (Google "angle of dip")

I believe compass manufacturers compensate for this with the bearing alignment so that the needle will swing freely (this is the reason why Northern hemisphere compasses don't work well in the southern hemisphere). So if your compass polarity is reversed the needle will drag indicating a reversal may have occurred. We commented on this at the time without realising the significance - in my original photo the faulty compass is the one with the white lanyard.

Does this make sense?

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Old April 26, 2013, 06:29 PM   #20
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I have done the resetting by stroking a needle with a magnent. It does work but it is easier said than done. I had to use two magments and there is a trick to it.
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Old April 26, 2013, 10:07 PM   #21
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A magnetic compass will be affected by close proximity to alkaline batteries such as Duracells. Storage in a backpack next to a flashlight and GPS will be enough to permanently affect the polarity of the compass needle/pointer.

To see if your electronic gizmos are affecting your compass, try the simple experiment of moving your flashlight, GPS, etc. close to the compass. If the needle moves, you've found the culprit.

If you're trying to find your way in low light or the dark, holding the light close to the map or compass will be enough to distort the compass reading by a large amount. That deviation will not always be the same, so it isn't possible to compensate for that "interference" alone.

In compass navigation it's useful to remember the nemonic for accuracy, "True Virgins Make Dull Companions": True, Variation, (from the compass rose on the map) Deviation, (from nearby metal or other interference) and Compass (reading).

Last edited by Shep; April 26, 2013 at 10:14 PM.
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Old April 27, 2013, 10:54 AM   #22
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Looking at your scenic view of New Zealand a second time. If caught off guard while in the bush with a broken compass. You could look for a tree and check and see if the moss is growing on its North side? ~~or is it the South Side down there? Now that I think about it. I'm not sure if you folks have a tree?_
One good thing about your conundrum though. New Zealand is indeed a island so you got to come out someplace on it with or without a compass. That's a +1._

Here in MN we have open pit Iron Ore Mining and tailing dumps to deal with that often emit magnetism to where at times the needle on my compass resembles the wife's kitchen blender. Were taught early on to watch where the Sun is located over our shoulders for direction. And walk a straight line. That's Old School teachings.
New way the Military way. Dependance on a compass is assured. If you don't get lost your at least going to be confused. i.e. Calculate distance, bearing between two latitude/longitude points. Topographical maps. Oh that was so much fun.___

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Old April 27, 2013, 05:06 PM   #23
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I'm a cheap SOB, and I hunted with a Silva compass that's polarity was reversed for years. As long as I knew it was reversed and it was consistent, it made little difference that it was the white end of the pointer showing North instead of the red. It wasn't until I cracked it somehow and the fluid leaked out that I broke down and bought another. I always checked it and every other compass I have owned in the last 40 years before I lose sight of the vehicle. Most times more than once. This tells me I can trust them before I NEED to trust them. I take a bearing on which way I'm headed when I leave and know that I need to be doin' the opposite to get back. The sun and the watch trick was taught to us in the Boy Scouts almost 50 years ago. Unfortunately, it only works when you can see the sun. But then, generally, if you can see the sun, you don't really need a compass, unlike when it's snowing, raining or just plain overcast.
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Old April 27, 2013, 06:27 PM   #24
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Consider a SPOT. They can be viewed at REI dot com. They are handy if you get lost as long as you have satellite access.
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Old April 28, 2013, 07:51 AM   #25
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As Kraigwy said, you can find South with an analog watch or you can make a rough sundial if you have a digital. Point the hour hand at the sun and halfway between the hour hand and 12 is relative South.
I often use this method, but it has limitations. The major limitation is that within the tropics, where I used to spend a good deal of time, you have to know were you are in relation to the equator and the relative position of your general latitude to that of the celestial latitude of the sun. Of course is you are in the extratropical latitudes of the Southern Hemisphere, the method renders North.

Having been a professional navigator for several years, you pick up all kinds of tricks. For gross reference at night, I tend to use Orion, if the Pole Star is not visible. In the Southern Hemisphere, Crux is valuable the same way.
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