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Venio
08-10-2007, 21:03
I know that Suunto balances their compasses in 5 different zones. However, when I tried to find a marking on my SK-5 there was none. I assume since it is bought in the US it must me Zone 1. Does anyone know how to find the zone for sure?

cummings66
08-10-2007, 22:39
That's an interesting question and I'm curious how it works. I know our declination varies a LOT depending on what part of the country you live in, as a pilot all of our charts show that data.

I know I've heard that in the US you can only buy the version meant for here and if you take it abroad it might not be too accurate. I know that can be true.

If you're wondering if it's usable here I'd suggest a quick test. Get a good brand name compass and compare the two of them and see how it comes out.

If there's a serial number I'd say that's how you tell, most manufacturers denote special countries of origin that way.

Krakenn
08-12-2007, 06:48
This is a bit of a worry lads.

Are you serious? _ I mean 99.999% of the time who cares but ?

Kraks

ScubaToys Larry
08-12-2007, 07:31
The compasses don't change for declination, they change for inclination. The way to see is put it on a flat level table, and see if the compass rose sits flat. If you take a northern hemisphere one to the south, it will just have a tilt to it, so you would have to hold the compass at a slight angle so as not to have the rose hit the glass. Really, not that big of a deal.

And true, depending where in the US you are diving, you might be 6 or so degrees off from true north - but it's not like you are flying from california to vermont. You are swimming a few hundred yards - so if you're off by a few yards... no big deal. And when people give you directions to stuff.. they are going to give you compass headings - so their numbers will be off too. Stuff like, "From our dock, take a heading of 300 degrees and swim 200 yards and you should find the sunken treasure." I wouldn't bother ask, "Is that with or without compensating for declination?"... Unless of course it was a very large treasure! :smiley2:

ScaredSilly
08-12-2007, 12:20
Depending on the water vis (and treasure) I think I would ask for the declination. A 6 degree declination will result in a 10% (sin 6) error which over 200 yards will result in a 60 foot deviance. In 40 foot viz that may mean no booty. In places like the Pacific North West and North East it is up to 20 degrees which will put you at almost 35% off.

ScubaToys Larry
08-12-2007, 12:23
Depending on the water vis (and treasure) I think I would ask for the declination. A 6 degree declination will result in a 10% (sin 6) error which over 200 yards will result in a 60 foot deviance. In 40 foot viz that may mean no booty. In places like the Pacific North West and North East it is up to 20 degrees which will put you at almost 35% off.


Yea, but the deal is, everyone else is dealing with the exact same thing. So you and your buddy say you are going to take a heading of 220, what does it really matter if in actuality it is 245? And to correct it, you would need a different compass anytime you went a few hundred miles in any direction. Now as soon as they have a DG for divers... that would be cool!

ScaredSilly
08-12-2007, 12:42
Yea, but the deal is, everyone else is dealing with the exact same thing. So you and your buddy say you are going to take a heading of 220, what does it really matter if in actuality it is 245?

In that case you are correct. I agree who cares. I was thinking in terms actually locating something like a wreck (or treasure). Now a days with so many things being located with GPS you have to be able to correct.

Like the guy who lost his anchors and comes in a says I'll pay you $100 to go find it. Here are the GPS lat long coordinates.


And to correct it, you would need a different compass anytime you went a few hundred miles in any direction.

Huh, people have been correcting for the declination for a long time with a regular compass. You just need to know the local declination and adjust acordingly by adding or subtracting from the true north reading. Map & Compass 101

Venio
08-12-2007, 13:03
Huh, people have been correcting for the declination for a long time with a regular compass. You just need to know the local declination and adjust acordingly by adding or subtracting from the true north reading. Map & Compass 101

Which bring back the original question about knowing for what zone the compass was balanced in first place. :smiley36:

Now if someone points me to an underwater GPS unit, it will be mucho appreciated!:smiley2:

Krakenn
08-13-2007, 08:40
Just dont get lost and dont do the Advanced Diver Course in the Southern Hemisphere!

Smiles

Kraks

tedtim
08-13-2007, 09:01
Depending on the water vis (and treasure) I think I would ask for the declination. A 6 degree declination will result in a 10% (sin 6) error which over 200 yards will result in a 60 foot deviance. In 40 foot viz that may mean no booty. In places like the Pacific North West and North East it is up to 20 degrees which will put you at almost 35% off.You must first have a good understanding of the units you are using. There is a difference between true north, magnetic north, and grid north. If you know which one you are using, then you can make the appropriate correction. I have not seen an underwater compass that allows you to make a correction; they all point to true north.

Other factors come into play over which you may have no control. For instance, if there is a large iron deposit near you underwater, it can cause your compass to have an error.

As for a 60 foot error.... unless you are in water that has absolutely no current, you can read your compass to a one degree tolerance, you have exceptional skills to maintain a heading to within a one degree tolerance, and you have full confidence in the accuracy of the GPS readings (which have an error in most basic systems), you will have track error.

You do have to adjust your heading for the effect of current, but by how much depends on the speed of the current.

This almost sounds like - measure with micrometer, mark with chalk, cut with an axe.

cummings66
08-13-2007, 11:42
Actually IMO there is but one method under water to navigate by, use deliberate error. That way you know for sure what side of the target you're on and can then head the right way towards it.

Oh, there's other ways as well, but I don't think underwater navigation is accurate for many reasons.

ScaredSilly
08-13-2007, 17:49
I have not seen an underwater compass that allows you to make a correction; they all point to true north.

I think you meant all compassed point to magnetic north - the corrections gets you true north.



I
Other factors come into play over which you may have no control. For instance, if there is a large iron deposit near you underwater, it can cause your compass to have an error.

Absolutely, once I got suck in the middle of some magnetite while on a backcountry ski tour during a white out storm - threw the compasses in the pack and navigated by terrain.


But you are correct underwater compasses are a bit of crap shoot. That said people should understand that there is sometimes more than just take a declination and follow it. But many times that is all you need.



Actually IMO there is but one method under water to navigate by, use deliberate error. That way you know for sure what side of the target you're on and can then head the right way towards it.

Oh, there's other ways as well, but I don't think underwater navigation is accurate for many reasons.

I like Brownian Motion

plot
08-19-2007, 21:47
Actually IMO there is but one method under water to navigate by, use deliberate error. That way you know for sure what side of the target you're on and can then head the right way towards it.

Oh, there's other ways as well, but I don't think underwater navigation is accurate for many reasons.

if i know the depth of what i'm looking for this what i do. purposely aim for the left of it then when i get to the correct depth, i turn right and usually it's right there.


a compass doesn't neccessarily have to be accurate, just has to point the same direction every time wherever you're at so you have a solid reference point. it could be pointing south, as long as it stays pointing south.... who really cares? (at least, when it comes to underwater navigation it shouldn't matter much)

ScaredSilly
08-21-2007, 15:19
I would prefer to have a compass that is both reasonably accurate (give the right direction) and precise (give the same direction every time). That way I can get us out there and my buddy get us back (in case one compass goes tits up during the dive).