Compass calibration ???

How important is it to have a compass calibrated to the Southern Hemisphere
( for mainly diving locally in Asut )...as opossed to one calibrated to the
Northern hemisphere ?

I've heard you just need to angle the later slightly when using it, as the
"pole" is pulled downward causing it to stick sometimes...

Like is it not that much of a drama ?



cheers,
Hi-Soft

"Hi-Soft" <bjcanham-nospam-@hotmail.com> wrote in message
news:47fee351$0$1218$5a62ac22@per-qv1-newsreader-01.iinet.net.au...
> How important is it to have a compass calibrated to the Southern
> Hemisphere ( for mainly diving locally in Asut )...as opossed to one
> calibrated to the Northern hemisphere ?
>
> I've heard you just need to angle the later slightly when using it, as the
> "pole" is pulled downward causing it to stick sometimes...

all compasses point to the North magnetic pole. Yes you need to keep any
compass "flat" because if the little arm thing ( and that is technical
speak ) isn't floating properly in the fluid it can catch on the case. Not a
matter or N or S hemispheres just a matter of mechanics.



>
> Like is it not that much of a drama ?
>
>
>
> cheers,
> Hi-Soft
>

Hi-Soft wrote:

> How important is it to have a compass calibrated to the Southern
> Hemisphere ( for mainly diving locally in Asut )...as opossed to one
> calibrated to the Northern hemisphere ?


As others in rec.scuba have pointed out, there are
subtle differences in declension between the Northern
and Southern hemispheres. And for that matter between
the Eurasian landmass and the North American landmass
or even between the East and West coasts of the US.

BUT -- and this is a big but... By the time you figure
in the effects of currents and all of the steel in your
kit (Particularly with twin 12l steel cylinders) you're
lucky to get anywhere close. Even a single steel cylinder
has a fair effect on the accuracy of compasses that I
have seen. The reality is that if you can navigate to
within 15-25 metres of your target underwater you're
doing well. And with good viz this is usually "good
enough"

IMHO, a precision compas underwater is like a scale that
reads out in grams and is accurate to the nearest 0.5Kg.

You're better off learning to "read" the sand ripples and
follow landmarks on most dive sites.
>
> I've heard you just need to angle the later slightly when using it,
> as the "pole" is pulled downward causing it to stick sometimes...
>
> Like is it not that much of a drama ?


I don't think so

-Don

"Don Gingrich" <gingrich@cs.rmit.edu.au> wrote in message
news:i4ydnYXD1oNzoZ7VnZ2dnUVZ_oOnnZ2d@internode...
> Hi-Soft wrote:
>
>> How important is it to have a compass calibrated to the Southern
>> Hemisphere ( for mainly diving locally in Asut )...as opossed to one
>> calibrated to the Northern hemisphere ?
>
>
> As others in rec.scuba have pointed out, there are
> subtle differences in declension between the Northern
> and Southern hemispheres. And for that matter between
> the Eurasian landmass and the North American landmass
> or even between the East and West coasts of the US.

all compasses point to magnetic N which of course varies over time and is
not the same as the N pole. Variations are not due to being in the N or S
hemisphere but to local factors. As your correctly point with all the metal
you carry diving small variations are irrelevant

"dechucka" <dechucka@vomithotmail.com> wrote in message
news:4803544d$0$30909$5a62ac22@per-qv1-newsreader-01.iinet.net.au...
>
> "Don Gingrich" <gingrich@cs.rmit.edu.au> wrote in message
> news:i4ydnYXD1oNzoZ7VnZ2dnUVZ_oOnnZ2d@internode...
>> Hi-Soft wrote:
>>
>>> How important is it to have a compass calibrated to the Southern
>>> Hemisphere ( for mainly diving locally in Asut )...as opossed to one
>>> calibrated to the Northern hemisphere ?
>>
>>
>> As others in rec.scuba have pointed out, there are
>> subtle differences in declension between the Northern
>> and Southern hemispheres. And for that matter between
>> the Eurasian landmass and the North American landmass
>> or even between the East and West coasts of the US.
>
> all compasses point to magnetic N which of course varies over time and is
> not the same as the N pole. Variations are not due to being in the N or S
> hemisphere but to local factors. As your correctly point with all the
> metal
> you carry diving small variations are irrelevant
>



Great...thanks for all the info... all is clear now :)

bc