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From: Ian Gregory on 4 Apr 2010 08:47
On 2010-04-04, Wes Groleau <Groleau+news(a)FreeShell.org> wrote:

> To me, a "magnetic compass" is a magnetized needle
> that turns to point to the magnetic pole (if no ferrous material
> is close to it. A magnetometer also depends on the earth's magnetic
> field, but not in the same way.

They are less different than you might think. A magnetometer measures
the strength of the local magnetic field. A three axis magnetometer
measures it in three orthogonal directions, from which both direction
and strength can be calculated. A magnetised needle will naturally try
to line up with the direction of the local magnetic field.

A digital compass based on a magnetometer should indicate the same
direction as a traditional compass and both should be affected in the
same way by "magnetic interference". I would describe them both as a
magnetic (as opposed to gyro) compass.

Ian

--
Ian Gregory
http://www.zenatode.org.uk/
From: Jeffrey Goldberg on 4 Apr 2010 14:57
Wes Groleau wrote:
> On 04-03-2010 22:16, Tim Adams wrote:

>> Is there an Apple store nearby where you could show it to
>> them and
>> perhaps get it replaced? It shouldn't be 'working' like you say it is.

> Bought it two days ago. Nearest Apple store is 200 KM.
> Though there's an "authorized repair" place here.
>
> There is no sign of any other malfunction.
> One person responded to one of my posts who apparently
> has seen similar behavior. Reports on the web that we're
> not the only ones.
>
> I think I will call Apple to see what they say.
> But for me, it's more of a curiosity than a problem.
> I don't need a compass.

You don't need it today. And even if you never need it, you may at some
point sell or give the thing away to someone who values that feature.

Try borrowing a traditional compass and do side by side comparisons. If
the iPhone compass is as bad as it appears from your tests, you really
should look into getting it replaced. (Also, I'm really curious about
the side-by-side comparisons).

Cheers,

-j


--
Jeffrey Goldberg http://goldmark.org/jeff/
I rarely read HTML or poorly quoting posts
Reply-To address is valid
From: Wes Groleau on 5 Apr 2010 02:24
On 04-04-2010 14:57, Jeffrey Goldberg wrote:
> Wes Groleau wrote:
>> I don't need a compass.
>
> You don't need it today. And even if you never need it, you may at some

Since maps work and GPS work, I don't need a compass.

> point sell or give the thing away to someone who values that feature.

That _is_ a possibility.

> Try borrowing a traditional compass and do side by side comparisons. If
> the iPhone compass is as bad as it appears from your tests, you really
> should look into getting it replaced. (Also, I'm really curious about
> the side-by-side comparisons).

I know from experience as well as from physics and electronics, that
one cannot even see the effect on a traditional compass made by nails
four meters away. The sort of errors mine is getting would take some
effort to produce in a 'traditional' compass.

--
Wes Groleau

Mexico Under Siege
http://Ideas.Lang-Learn.us/russell?itemid=1534
From: Wes Groleau on 5 Apr 2010 02:34
On 04-04-2010 04:23, ZnU wrote:
> The Earth's magnetic field is a couple of hundred times weaker than a
> refrigerator magnet. It doesn't take a lot to interfere with compass
> readings.

This is true as stated. But it _does_ take a lot to get the sort of
errors I've described. Especially the one where it pointed northwest
for several minutes then shifted to north when the closest change in
environment had been my breathing three or four meters away.

> Anyone who follows Apple news is used to the whole notion that as soon
> as Apple does something, people start inventing new standards, that no
> other vendor has ever met, that they can criticize Apple for not
> meeting. But doing this with a technology as old as the compass seems a
> little over the top.

I'm not inventing new standards. I know what can interfere with a
'traditional' compass, and how to avoid it. What's happening with
this one is completely different. I wasn't really criticizing one
of my favorite companies--though I suppose one could say it's not like
Apple to hype a feature that is useless. But then one could answer
(and some have) that it actually works well for most people, and I
should get my device repaired.

>>>> (2) I have been in two Doge vans and one Cadillac that had
>>>> consistently accurate compasses in spite of the vehicle's
>>>> composition.
>>> Which, being built into those vehicles, are presumably designed to avoid
>>> that interference.

While mine is apparently producing its own interference. :-)

--
Wes Groleau

Race Doesn?t Matter
http://Ideas.Lang-Learn.us/WWW?itemid=876
From: Wes Groleau on 5 Apr 2010 02:36
On 04-04-2010 06:04, Tim Streater wrote:
> Just like any other compass, then. C'mon, you should know better than
> this.

Sounds like you have little experience with "any other compass."

Or you have improperly assumed I'm attacking Apple and jumped
to their defense without bothering to read the alleged attack.

--
Wes Groleau

Words of the Wild Wes
http://Ideas.Lang-Learn.us/WWW
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