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Storing Compasses Properly

6:29 p.m. on November 3, 2010 (EDT)
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I was looking at several compasses today and started thinking about how to properly store them.

Since compasses can affect one another's readings if too close to each other or some other magnetic force, I wondered if they would be affected long-term if stored with or near other compasses.

If you store a couple of compasses together, can that throw them out of whack long-term? Or is it just a temporary effect while next to each other?

And if they do affect each other, how much distance is needed for the compasses? How much exposure is too much?

Any ideas?

Any other suggestions about what not to store your compass near, besides obvious magnets?

 

8:07 p.m. on November 3, 2010 (EDT)
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I was looking at several compasses today and started thinking about how to properly store them.

Since compasses can affect one another's readings if too close to each other or some other magnetic force, I wondered if they would be affected long-term if stored with or near other compasses.

Short answer - yes, most definitely

If you store a couple of compasses together, can that throw them out of whack long-term? Or is it just a temporary effect while next to each other?

Depends on how close together and the nature of the two compasses, but the effect is long term. Some compasses, especially high-quality compasses and compasses for orienteering competitions, have very strong magnets. Placed against an inexpensive compass, the inexpensive compass has a high probability of having its magnetism reversed or diminished. The compasses with high-intensity needles are generally not as affected.

Flux-gate compasses (the electronic ones) can become de-calibrated easily by the presence of even small external fields, such as the fields present in a car from the electric system, remote car locks, generator/alternator, and so on. That fluxgate compass in your car's rear view mirror is better shielded, but it can get decalibrated - look in your car's owner's manual for the calibration procedure (basically it is just driving slowly in a circle).

And if they do affect each other, how much distance is needed for the compasses? How much exposure is too much?

Any ideas?

Luckily, for quality compasses, the distance is fairly small, just a few inches. If you look on the Suunto, Brunton, Silva (Sweden), and JWA Silva web pages, you can look at their teaching and competition packages, where they show images of the boxes for storing sets of training compasses to get an idea of the spacing the manufacturers themselves use. It does make a difference, as well, how many of the compasses you pile into the box on top of teach other and their orientation. Placing them parallel allows the needles to swing so the magnetic fields can align, which keeps the fields stable.

LARGE_compbox_field7.jpgOne of Silva's (Sweden) training kits, with the small baseplate compasses.

 

 

Any other suggestions about what not to store your compass near, besides obvious magnets?

 

As mentioned, electric currents and magnetic fields are intimately connected (we are all supposed to have learned this in our grade school science classes, or in high school physics). So think about where you put your compass in the car, or near electrical gear at home (like the refrigerator's electric compressor motor), or high voltage transmission lines (you should be ok if you don't climb up the towers, which introduces another risk factor - don't touch the power lines!).

Speaking of refrigerators, those "supermagnets" that everyone uses to hang notes on the refrigerator door will change the magnetism of your compasses needle.

All that said, there is a "magic trick" to realigning your compass. Basically, you place a strong bar magnet with its north pole next to the compass and leave it there for a few hours. You can also pass the magnet over the compass housing with the magnet's north pole (more correctly "north-seeking pole"), moving it almost in contact with the capsule from the middle (over the pivot) along the compasses needle, lift a foot or so above the compass, loop back to above the pivot, lower, and repeat the circle a few times. This should do it.

Once when I was teaching a basic map and compass map course, a friend (who had organized the course) and his wife showed up with her compass pointing in reverse. Since he knew this trick, he did the procedure that evening with a magnet he had at home, and she showed up at the field exercise the next morning with the compass working just fine.

I do not recommend you reverse the compass needle on a good compass just to try this out. Do it with one that already has the problem. That way, since it may take a few tries to get the technique down, you have nothing to lose.

By the way, do not forget that (1) the red or blue end is the one that is supposed to point north (the coloration varies with the manufacturer, with the south end being left uncolored usually); and (2) the compass needle is balanced for a particular magnetic "dip" zone (most of the Northern Hemisphere is "zone I", with Australia in "zone V"); if you look closely at the needle, you will see a small hole (reduces the weight of that end of the needle) or a small weight (added weight to that end) to compensate for the dip in the Earth's magnetic field (the tilt from horizontal). If you are using a compass in the wrong zone, one end of the needle will rub against the capsule and make the compass seem slow or even non-responsive.

4:45 p.m. on November 16, 2010 (EST)
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Thanks, Bill. I don't have any flux-gate compasses, so those aren't an issue. I was mainly thinking about this in reference to some old compasses we have in our collection.

I was putting them out on a shelf in my office to display them, but then started wondering how close was too close.

If a compass has its polarity reversed that would (or should) be very obvious and I understand how to reverse it back (though I've never done so).

But what about if it's diminished by a stronger compass? Does that mean the reading is going to be slightly off? And if so, how would you even know, without comparing it to a working compass or known direction?

6:55 p.m. on November 16, 2010 (EST)
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There are several indications. Most obvious is in comparison to another compass (sooo, which of the 2 is off? - the old two answers, which of the 2 is right conundrum). If you are in a known location, you can determine if the compass is off easily. At night, if it is clear, take a bearing of Polaris (or use the Southern Cross to locate the south point of the horizon in the Southern Hemisphere.

Another way is to pick two points 50 to 100 meters apart and take bearings from one to the other, then go to the second point and take the bearing in the other direction. They should be 180 deg apart. Partially demagnetized compasses will give inconsistent readings. But a partial demagnetization that is skewed is very rare. Usually it shows up as a "jittery" needle.

The problem our friend Janet had was a complete reversal of the N and S ends of the needle. That was spotted only by everyone else in the group getting a bearing that was 180 deg different (plus we had a map of the area and plenty of easily recognized landmarks).

The most likely problem is a damaged bearing, in which case the needle will barely move or will be "sticky" as you rotate the body of the compass.

The other thing in displays is that if the compasses are too close, the 5 compasses (to pick a random number) will point in 5 slightly different directions. How "slight" depends on how close you put them. The other thing in a lot of display setups is not realizing that the table has steel or iron fastenings close to where the compass is placed. Lights for illumination use electricity, of course, so if the lights are in the wrong position, the magnetic field generated by the electricity feeding the lights (including the cord) can make the compasses deviate as well.

I took a photo of 5 compasses on the patio for a slide for my land nav class (nice "rose" sandstone flagstones, great background), forgetting that the slab had iron rebar throughout (which can sometimes be magnetized). And there was the group of scouts I took on a training hike, divided into groups of 3, handed them maps, and said figure out your route. One of the groups set their map on a convenient fairly flat surface and diligently studied it, looking around at the landmarks to orient the map and couldn't figure out why the map and landmarks were in disagreement. The other adult leader and I watched for about 10 minutes, then decided we ought to remind them that the hood of a car is made of steel and sits over an engine made with an iron block (in this case).

9:53 a.m. on November 22, 2010 (EST)
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Thanks, Bill.

 

2:29 p.m. on November 22, 2010 (EST)
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Is there a lifetime limit to a compass? I mean do they eventually lose their proper magetivity or do they last indefinately?

I still have my original Boy Scout compass that I got when I was 12, thirty three years ago. Its the flat plastic kind with the compass dial on one end and a numerically marked other end. It has a measure ruler on one side also.

Tho I rarely use it anymore for directions or map reading, it has more a nolstagic ownership for me, I think of when I first learned in scouts how to use it.

5:20 p.m. on November 22, 2010 (EST)
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Is there a lifetime limit to a compass? I mean do they eventually lose their proper magetivity or do they last indefinately?

Depends on the compass. Top quality compasses, stored under reasonable conditions, will keep their magnetism indefinitely. I have one of my father's compasses that was made around 1900 which works just fine. It lacks some modern refinements, like liquid or eddy current damping. But it is as accurate as as any of the other quality pocket compasses I have. A collector friend has several ship's compasses from the 19th Century that are right on. I have seen exhibits in museums with some of the earliest compasses made for surveyors and sailors, which appear to be in perfect working condition.

OTOH, I have a group of "toy" compasses that were in a kit for teaching about magnetism in physics and survey physical science classes where no more than 2 point in the same direction, though there are several that seem to be paired. When I got them for the "physical sciences for the non-major" course I was teaching at the time (mid 1960s), they were just fine for tracing the magnetic field of a straight wire or coil. They were something like $5 for a pack of 20, I think, and about 3/4 inch in diameter.

11:07 p.m. on November 22, 2010 (EST)
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OTOH?

8:54 a.m. on November 23, 2010 (EST)
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OTOH?

On the other hand

1:49 p.m. on November 23, 2010 (EST)
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Thanks I was stumped too.

2:43 p.m. on January 14, 2011 (EST)
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I had a reasonably priced walmart compass that changed polarity.  Fortunately, I was in a place where I knew north and south so the 180 degree shift in the north direction caught my atention.  The error was not based on influence in the area hiking.  The best I could figure was that I normally store my compass and pocket knife together in the same belt pouch.  I now store them separately and check the polarity based on some know map direction before going into the woods where the shift in polarity could be fatal.

3:39 p.m. on January 14, 2011 (EST)
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To quote a drunk sprite from Willow:

"WE GO THAT WAY!!"

*points wildly in the wrong direction*

8:55 p.m. on January 14, 2011 (EST)
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Haha...I remember that scene.

Welcome Mountain Dog, fatal polarity is bad.

April 19, 2014
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