How To Calibrate A Compass?

[Blandeena]

is there anyway to calibrate a regular(non digital) magnetic compass? I have a bunch of compasses and they all point in different directions, and it'd be nice if they all pointed in the correct direction instead hehe. Thanks for any help/suggestions!

[+Renegade Knight]

Edit: Worthless method deleted. A better one is below.

Edited November 4, 2004 by Renegade Knight

[+amytincan]

there's some with a little tiny screw that has something to do with calibrating. We had to do this way back when I worked for the USFS.

 

can you check on the website? Silva Website

[Bobthearch]

The compass needles should all point the same direction if they're magnetic. If they don't, then operator error is the most likely explanation - holding the compasses near each other or against a beltbuckle for instance.

 

There is no way to 'calibrate' the Earth's magnetic field, or a magnet's attraction to it...

 

there's some with a little tiny screw that has something to do with calibrating

 

You're talking about the magnetic declination adjustment. It changes how the numbers on the baseplate match up to the magnetic arrow - it can't alter the direction that the arrow actually points.

 

Best Wishes,

Bob

[+amytincan]

The compass needles should all point the same direction if they're magnetic. If they don't, then operator error is the most likely explanation - holding the compasses near each other or against a beltbuckle for instance.

 

There is no way to 'calibrate' the Earth's magnetic field, or a magnet's attraction to it...

 

there's some with a little tiny screw that has something to do with calibrating

 

You're talking about the magnetic declination adjustment. It changes how the numbers on the baseplate match up to the magnetic arrow - it can't alter the direction that the arrow actually points.

 

Best Wishes,

Bob

well it has been abuot 14 years.

[+Beta Test]

The compass needles should all point the same direction if they're magnetic. If they don't, then operator error is the most likely explanation - holding the compasses near each other or against a beltbuckle for instance.

 

There is no way to 'calibrate' the Earth's magnetic field, or a magnet's attraction to it...

 

there's some with a little tiny screw that has something to do with calibrating

 

You're talking about the magnetic declination adjustment. It changes how the numbers on the baseplate match up to the magnetic arrow - it can't alter the direction that the arrow actually points.

 

Best Wishes,

Bob

Yes compasses acn be calibrated. How do the magnetic compasses in US warships ( yes theyre there) point North when surrounded by steel? I've had compasses completly reverse directions before, and slowly go back to normal. I had one compass in one spot away from anything magnetic, and the "North" needle pointed south. Placed the other in the same spot and the needle pointed 180 degress in the other direction.

 

This post was not meant in the unfriendly tone that it probably seemed when you read. Again this is a friendly toned post

[Bobthearch]

Yes compasses acn be calibrated. How do the magnetic compasses in US warships ( yes theyre there) point North when surrounded by steel?

Wow. That never crossed my mind. My car compass can be calibrated, but I'm pretty sure it's electronic. I don't think you'll calibration capabilities in handheld compasses.

 

I've had compasses completly reverse directions before, and slowly go back to normal.

That's very strange. I've used hundreds of compasses and never seen anything like that. I suspect the arrow became de-magetized, but I don't really know.

 

I had one compass in one spot away from anything magnetic, and the "North" needle pointed south.

I bet the compass was reacting to ~something~ in that spot - a piece of metal, something electronic, or perhaps an underground water line. That falls under the category of Operator Error. Some compass magnets are more sensitive, which might explain why the other compass wasn't affected.

 

Still, there's no way to recalibrate a handheld compass. That I know of...

 

You post didn't sound unfriendly at all. But I'm immune to that anyway after years of being a jerk myself.

 

Best Wishes,

Bob

[+MaxEntropy]

Yes compasses can be calibrated. How do the magnetic compasses in US warships ( yes theyre there) point North when surrounded by steel?

 

Ships don't really use magnetic compasses. They have gyrocopasses which always point to true north once set-up and precessed properly. Since you never bet your life on technology, they also carry magnetic compasses as a back-up

 

The marine "standard" magnetic compass is adjusted to compensate for the metal of the ship by adjusting the fore-and-aft and athwartship magnets, quadrantal spheres and the Flinders bar. Even then some deviation will still exist so a deviation table is required from which you can finish correcting your compass course.

I doubt that there is a pocket compass that is equipped with any of these so it's better to simply keep it away from iron, DC wiring and other magnets.

[Blandeena]

Oh wow, a bunch of info about compasses. Some pretty interesting facts. I was just hoping there would be a way to 'retrain' a compass needle to point north again.

[bug and snake]

Oh wow, a bunch of info about compasses. Some pretty interesting facts. I was just hoping there would be a way to 'retrain' a compass needle to point north again.

Well, you know, there kinda is, but the truth is that the process is so convoluted that it is not worth the effort. IF and ONLY IF the needle has lost it's magnetism you can remove it, or lock it in position, and re-magnetize it. It's easier, more reliable and generally cheaper to just get another compass. As many of the above posts have said, keeping the unit you are using away from undue influence when in use is the most important thing. I have actually seen people bring out a compass and lay it on the hood of the car and then complain that it isn't pointing in the right direction.

[+briansnat]

Oh wow, a bunch of info about compasses.  Some pretty interesting facts. I was just hoping there would be a way to 'retrain' a compass needle to point north again.

There is no need to calibrate, or re train a magnetic compass because a decent magnetic compass always points north. If you are comparing them side by side they may be affecting each other's magnetic field. As others pointed out things like proximity to metal, even a belt buckle, could throw them off.

 

Also, they can be thrown off in areas with heavy iron deposits in the ground.

[bug and snake]

There is no need to calibrate, or re train a magnetic compass because a decent magnetic compass always points north.

That's my point exactly - stated much more clearly than I said it.

 

Quote: 'It's easier, more reliable and generally cheaper to just get another compass.'

 

If your compass needle has lost its north seeking ability then it most probably was a pretty poor compass to start with.

[+Gonzo-YT]

Compasses are one thing that you definitely get what you pay for... For instance, I like to leave those little keychain compasses in geocaches. I bought about ten of them at once and I think that none of them actually pointed North, although most were close -- 10-15 degrees, anyways.

 

As far as I can tell, it is more a problem with manufacture than magnetism. If the needle isn't level and able to move freely, it can't do its job.

 

Others have also made good points here about keeping it away from metals, electronics, etc. Don't tape it to the bottom of your GPS.

 

If you're serious about working with a map compass, Brunton Type 15 (or comparable model from another company) is the only way to go.

[Bobthearch]

Ships don't really use magnetic compasses. They have gyrocopasses which always point to true north once set-up and precessed properly.

Wheh! Thought I was going crazy!

 

If you're serious about working with a map compass, Brunton Type 15

Sorry for veering OT, but I've had mixed luck with Brunton-brand compasses. Some were OK, others were not. The biggest issue with Brunton is that the numbers are merely painted on, rather than etched into the base. Disappointingly, this was a problem with even their expensive models.

 

After twenty-plus years of honing map-and-compass skills, including twelve years that I field mapped thousands of archaeological sites, I propose this as the perfect compass for general use:

Suunto M3

 

These are about $20 at Foresty Suppliers, about the same price as buying a 'toy' compass at a local sporting good store.

Suunto M-3 at Forestry Suppliers

 

Very affordable, easily replaced, durable, accurate, and enough features for anyone not requiring professional survey equipment. If you need more than this, you probably need a transit and laser tripod.

 

Sorry for wandering so far off topic! Maybe someone will find this helpful. Maybe some GPS experts would like to become more familiar with the old-fashioned-way of navigating...

 

Best Wishes,

-Bob

[Blandeena]

Hehe yeah think it's time to get a new compass. Guess mine were all 'toy' compasses. Thanks for all the info!

[Bobthearch]

Hey Blandeena,

My compass recommendation is above. But here are some tips for selecting a compass in case you want to shop around:

- don't spend too much

- check to see numbers are etched into plastic, rather than just painted on

- look for magnetic declination adjustment screw on bottom of base ('toy' compasses don't have this)

- look for a brand with a good warranty

 

And tips for using compass:

- set declination according to your area - correct setting can be found on the bottom of USGS maps

- hold at waist-level, looking down on compass, then look straight up - don't hold compass up to your face unless it's a mirrored sighting compass (expensive and unnecessary)

- keep two or more distant objects aligned to walk in a straight line

- don't hold near metal or electronic objects

- use tape measure in parking lot practice your 'pace' - how many steps do you need to count to walk 100'? In real life, adjust the numbers to account for slope, walking around objects, and terrain.

 

Pick up a couple of USGS topo maps to practice with. They're about $6 ea.

 

When you're ready, move on to more advanced practices, such as triangulation. Then get out to the wilderness! There's no subsitute for experience...

 

Best Wishes,

Bob

[Taxman003]

there's some with a little tiny screw that has something to do with calibrating. We had to do this way back when I worked for the USFS.

 

can you check on the website? Silva Website

Depends on the model, but I have a Sunnito compass that I purchased for $ 70.00 and it too has a screw that is supposed to be used to account for some variance depending on where you are on earth.

 

Don't think most compases have this feature though.

 

Mike

[Bobthearch]

account for some variance depending on where you are on earth

Like I said, that adjusts for the magnetic declination. Magnetic North and True North aren't the same thing. As I recall, Arkansas is about 4 degrees off, while in New Mexico the declination ranges from 10 - 12 degrees.

 

Don't think most compases have this feature though.

I think it's safe to say that most quality compasses do have a declination adjustment scew. No, you don't find it on el-cheapo models. Without a built-in declination adjustment, you can do one of two things: 1) pretend there's no such thing as "magnetic declination" and ignore it, or 2) add or subtract the appropriate number of degrees every time you take a reading.

 

In Arkansas or east, you'll probably do fine with #1. In the West, 10 - 15 degrees is too significant to ignore.

 

Best Wishes,

Bob

Edited November 4, 2004 by Bobthearch

[+Criminal]

There's a nice new Silva Ranger CL in the Mt Col Bob cache, about nine miles round trip. (Unless someone grabbed it and didn't say so in the log)

[+AtoZ]

Sorry if this is said before but your can not check 2 compuss side by side as their inherit magantism will affect the results. To check pick a point on the horizon with one and then take a bearing with one compass then do the same with another compass and your see they should be the same. Only on a ship or some such big steely object is calibration need. If you look at a ships compass your see either 2 large metal balls that are moved to true the compuss or some times small magnets are used inside the compass housing. But terresstial compass do net need calibration.

cheers

[+rusty_tlc]

I didn't read every post carefully so I hope I'm not repeating.

A hand held compass is what it is. I have an antique that has a damping adjustment, but that has nothing to do with calibration.

A compass intended to be mounted in a ship, airplane or car can indeed be calibrated. Actually aligned. This is necessary to compensate for the distortion of the earths magnetic field by the engine and body. This type of compass has small internal magnets which can be adjusted by screws to alter the home position of the needle. The traditional method of aligning these compasses is to point the vehicle due north by means of an external reference. Then the screws are adjusted until the needle points due north.

[+Gonzo-YT]

Hi Bob,

 

After twenty-plus years of honing map-and-compass skills, including twelve years that I field mapped thousands of archaeological sites, I propose this as the perfect compass for general use:

Suunto M3

 

Actually, I had seriously considered buying a Suunto, they make nice compasses. I prefer to use a mirrored compass myself, and in my case the deal-breaker was that the Type 15 has 1:50,000 and 1:250,000 UTM grid roamers on it -- essential for using Canada topo maps. The comparable Suunto at my local store had US scales.

 

I don't know about the etching vs. printing issue, I'll take a look at mine when I get home.

 

Although I was slagging keychain compasses in my earlier post, I do have a little Suunto Gem compass that I really like.

 

Regards,

Anthony

Edited November 5, 2004 by Gonzo-YT

[+writer]

This probably isn't the issue, but compasses are tuned for particular parts of the world. So one sold in, say, Australia is unlikely to work well in North Dakota. It's an issue of balancing the needed so that the pull of the earth doesn't bind it, causing faulty readings. You can get one that will work in any part of the world, but they require adjustment, are expensive, and can be, from what I understand, pretty finicky and sensitive to abuse.