Compass consistly off by 10˚ w/o interference source. Has been calibrated.

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Level 2

154 points

Compass consistly off by 10˚ w/o interference source. Has been calibrated.

I have noticed lately that my compass is off by approximately 10 degrees. This is a consistent error and I have tried the calibration steps multiple times. Just now, to be sure before posting, I stepped out to the end of my driveway and made sure I was as far away as I could be from a source of interference. Comparing to a reliable compass I own, I get about a 10-degree ENE deviation on the iPhone.

To answer one of the questions I know is coming: it's set to magnetic because that seems to match Google Maps better than true (interestingly enough) and it was the most accurate way to check against my compass. It was interesting that the declination was added correctly by the iPhone. I wonder it's "smart" enough to use GPS coordinates to accurately apply declination.

This is a functionality I'd love to have as I easily get turned around while walking when I head into town and it would be nice to know which way to walk without having to take a few steps to get the GPS going and then turn around. No to mention, orienting the map in the direction of travel is pretty useful).

3.06GHz iMac (4Gb RAM), Mac OS X (10.5.7), Other : Macbook, Mac Mini (HTS), iPhone 3GS (16Gb), Time Capsule (500Gb)

Posted on Jul 13, 2009 7:47 PM

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Answer 1

w7ox

Level 4

2,407 points

Jul 13, 2009 7:59 PM in response to Xian Rinpoche

Within 10 deg is about all I would expect from a magnetic compass housed in a device including electronics and a battery. Currents within the unit can affect it.

And for most uses I'd put it to, 10 deg from the iPhone's compass is good enough. I also have a compass in my wristwatch (Casio Pathfinder) which I figure might be good to 5 deg. For serious map-compass navigation I use a mirrored Suunto M2-G; with practice I can do about 2 deg with that.

Phil

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Answer 2

Macaby

Level 3

923 points

Jul 13, 2009 8:55 PM in response to Xian Rinpoche

Xian Rinpoche wrote:

It was interesting that the declination was added correctly by the iPhone. I wonder it's "smart" enough to use GPS coordinates to accurately apply declination.

Not to be nick picking, but it's called deviation (east or west). There used to be an old flying expression that said (East is least and west is best). A trick to keep track of which one is minus (east) and which one was positive (west).

And yes, the only way the IP could correct toward the right calibration is through "Maps". As far as I know, GPS in itself does not know what deviation should be for an area. However, coupling GPS with a map base would allow the IP to know how to compute true direction from mag direction.

Show me a hand held mag compass that is correct within 10 degrees and I say you have a pretty good mag compass.

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Answer 3

Xian Rinpoche Author

Level 2

154 points

Jul 13, 2009 9:51 PM in response to Macaby

Macaby wrote:
Not to be nick picking, but it's called deviation (east or west).

No, it's Magnetic Deviation.

Edit: To clarify, this is such a thing as Magnetic Deviation, but it has to do with local magnetic fields (such as the hull of a ship or a nearby iron ore deposit), as opposed to declination which is the difference between true North and the Earth's magnetic pole at a specific Lat&Long, expressed as an angle. Declination is what's used to determine True North from Magnetic. Check out a declination map sometime and you'll see it. I believe USGS quads also give declination.

Thanks for your other comments tho 🙂

(PS Also, the phrase is "nit-picking")

Message was edited by: Xian Rinpoche

Message was edited by: Xian Rinpoche

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Answer 4

ManuCH

Level 1

123 points

Jul 13, 2009 10:36 PM in response to Xian Rinpoche

If you're still in nit-picking mood, read this article for the differences among magnetic declination, deviation and variation:

http://en.wikipedia.org/wiki/Magnetic_declination

Magnetic variation and declination are synonyms, it just depends in what context they are used (ie. air navigation vs. others). These both refer to "how much the Earth's magnetic field is off if compared to true north".

Magnetic deviation is the interference caused by local magnetic fields (ie. the hull of a ship).

That said, I also find my iPhone 3GS' compass to be off by 5-10 degrees.

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Answer 5

Macaby

Level 3

923 points

Jul 13, 2009 10:42 PM in response to Xian Rinpoche

It looks like you're right and perhaps I'm partly right IF deviation is induced by a local magnetic force (say from the IP itself). As to nick-picking, a typo that I should have caught.

I spent 20 years as an Air Force Navigator and from day one in Nav School, we were taught to think of declination as "variation". My memory is a little cloudy now as that was a long time ago and I confused variation with deviation. I don't remember ever hearing the term declination except as a measurement of a heavenly body's position above or below the equator. Declination was an entering argument for computing a position based on observing how high the body was above the apparent horizon with a sextant. A good navigator could determine an airplane's position within 5-10 miles strictly with a sextant and that was good enough half way between LA and Hawaii in yesteryear.

So, if I were on a flight and the local declination (variation) was 20E and the desired heading was 90 degrees true, we steered 70 degrees magnetic unless we also had some deviation which might add or subtract 1-2 degrees to the desired heading. Maybe the Air Force was using the KISS theory by using "deviation" for declination. In case you're not familiar with KISS, it stands for "Keep it simple, stupid". Or don't confuse me with facts.

I do have what I think is an accurate mag compass (designed to taking bearings from a boat.) Comparing a heading taken from the compass with the compass in the 3G S across our lake, the IP compass reads about 15 degrees higher. Assuming my other compass is totally accurate, my 3G has a 15 degree right "deviation".

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Answer 6

Xian Rinpoche Author

Level 2

154 points

Jul 13, 2009 11:01 PM in response to Macaby

No, I think you were taught right to use "Deviation." My understanding has always been that deviation is critical when you're in a situation of some sort where there is some sort of interference from ferrous objects. Declination is a "raw" measurement that completely ignores things like the hull of a ship or the fuselage of a plane. I was in the Army and declination was critical during land-nav, but deviation was more a case-by-case basis I guess (I never heard of it in boot). But we were just humping it and didn't have to worry about being in a metal "can."

As for the astronomical reference, I have the feeling that's closely related. In my mind, at least, magnetic declination is simply astronomical declination in a horizontal plane (if that makes sense).

In the end, the term I used at first (declination) was the correct term for determining the difference between magnetic and true North on the iPhone. Your comment about deviation was also correct in that it takes an even more precise survey of the surroundings. You're never going to be able to put a bomb through a window using just declination. 😉

Hope that makes sense.

As for whether the USAF was using KISS, I would say that the Army is second only to the Marines in the KISS department. If we learned it in the Army, you probably heard it in the AF. Most likely, the Air Force said "Hey, there's an even more precise measurement here. Let's use it and teach it our people so we're able to put a bomb on a fly's head from 10000 ft while traveling 400 knots." The Army just figured you did a good enough job if you were within 300 yds of the target at running speed. 😉

Message was edited by: Xian Rinpoche

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Answer 7

Xian Rinpoche Author

Level 2

154 points

Jul 16, 2009 11:13 PM in response to Xian Rinpoche

Well, well. I exchanged my iPhone today for a new one (battery life was only about 70% of what specs suggested) and a quick test of the compass shows an error of only 2-3 degrees. This iPhone was made in Week 28 (versus Week 21) for my first. I'll obviously have to play some more, but it's almost dead on. Nice 🙂

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Answer 8

w7ox

Level 4

2,407 points

Jul 17, 2009 4:30 PM in response to Macaby

Macaby wrote:

Show me a hand held mag compass that is correct within 10 degrees and I say you have a pretty good mag compass.

I have four such (Silvas and Suuntos). In skilled hands can do 3-4 deg with reliability (I teach and examine land navigation).

iPhone 3GS: 10 deg is pretty good.

Phil

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Answer 9

Xian Rinpoche Author

Level 2

154 points

Jul 17, 2009 4:57 PM in response to KartM

KartM wrote:
Dont worry. its a phone and the compass is giving you a good idea of what direction you are facing.

Only if everything is at 90 degree angles. I think of several places in downtown Fort Worth where a reading that was off by 20+ degrees could be confusing. (If you're curious, find the intersection of Throckmorton St and W 9th St).

I agree that "it's a phone" but it shouldn't have a compass if it can't get reasonable accuracy. Apple is not known (so far) for poorly-implemented gadgetry. I'm going to keep testing and see if it gets better.

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Answer 10

Macaby

Level 3

923 points

Jul 17, 2009 5:27 PM in response to Xian Rinpoche

The IP is a great piece of equipment, but it can't be great at every single feature. If I were to take you out and leave you in the middle of nowhere, with your IP compass, you would probably be able to walk out to somewhere, but don't think you can find "Bluebeard's" treasure with it. Think of the compass feature like that telescope you got for your 6th birthday. Yes, it did magnify, but you weren't going to find any new constellations with it.

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Answer 11

Xian Rinpoche Author

Level 2

154 points

Jul 17, 2009 5:32 PM in response to Macaby

The way things stand right now, if you dropped me in the middle of nowhere with my iPhone, I would use a stick in the ground before I'd rely on this thing. 😉

Apple either completely caught the "gimmick bug" or there's a defect. it is interesting that this compass has been both more and less accurate than the one in the iPhone I originally started this thread about. I hope I don't have to return a 3rd :P

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Answer 12

Macaby

Level 3

923 points

Jul 17, 2009 5:50 PM in response to Xian Rinpoche

I predict if Apple gets a LOT of returns for compass not pointing correctly, they will stop allowing returns for that reason and if they could "delete" the compass feature on a software upgrade, they might choose to go that route also.

Hey, its just a phone. If you really need it as a compass and you got a 10 or 20 or 30 degree error, apply the correction and move on. With the GPS and Maps going, you can get a pretty good idea of your heading by watching the blue dot move.

Don't tell me you bought the 3G S ONLY because it came with a compass that you intended to use for geocaching or land surveying.

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Answer 13

w7ox

Level 4

2,407 points

Jul 17, 2009 5:56 PM in response to Xian Rinpoche

Xian Rinpoche wrote:
The way things stand right now, if you dropped me in the middle of nowhere with my iPhone, I would use a stick in the ground before I'd rely on this thing. 😉

Well, if the stick had a N-E-S-W set of arrows, good idea 🙂 We have one on a local pier.

My take is that it is good enough to tell me if I'm going North, West, South or East. If I emerge from a metro station in Paris, it will tell me which way I should walk to get to my hotel (did that once without a compass and walked 5 blocks, with bag, in the wrong direction).

I believe the 3GS compass has definite value. Mine has never been off by more than 30 deg in any place I've tested it .. and often is better than 10 deg.

Would I use it for serious land navigation? No way!

Phil

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Answer 14

Jul 17, 2009 6:06 PM in response to w7ox

What the heck, I'll pipe in too...

I used the compass once (and by once I mean over a 2-day period): I went to Philadelphia, PA for an overnight stay; using maps with GPS and compass (having it rotate the map so it matches the phone's position) was great - kept me from having to look at the sun to know which way was north. (Too bad I forgot to try pedestrian directions and didn't have a Nike+ device at the time.)

It might have been off by 5-10°, but it wasn't noticeable (not until I think back about it now). BUT, Philly's mostly 90° grid, so that wasn't an issue.

PS: ° = Option-Shift-8; my wife remembered it from when she did her biology thesis on a Mac.

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Answer 15

KartM

Level 1

65 points

Jul 17, 2009 6:08 PM in response to w7ox

w7ox wrote:

George Steinmetz wrote:
kept me from having to look at the sun to know which way was north.

Good thing: Best not depend on the Sun shining there 🙂

Phil

Ya the sun will explode in a billion years. We will need out iPhones to nagivate the heck out ;D
Back to topic: I am positive the compass on the phone will never be perfect. Just use some observational skills along with the compass to figure it out accurately.

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