Oslo, Norway magnetic declination and compass question

4:48 p.m. on February 4, 2003 (EST)
(Guest)

I will be taking some compass bearings around Oslo, Norway. I have two questions.

1. Should I use my compass purchased here in the eastern U.S. or purchase one locally? I have read that a compass bought in North America may not be accurate in South America. Is that a northern vs. southern hemisphere issue or is there more to it, like just being on a different continent?

2. How would I find the magnetic declination in Oslo, Norway? I have had no luck in my searches on the web. The reason that I ask before I purchase my topo map there is that I have heard that they sometimes use a system with 400 degrees instead of 360 degrees. Since I don't read Norwegian, I don't want to make a mistake.

7:53 p.m. on February 4, 2003 (EST)
(Guest)

Declination in Oslo : 2 degrees W

10:19 p.m. on February 4, 2003 (EST)
(Guest)

a.k.a. trout-chaser

Thank you, Ridgerunner.

3:11 p.m. on February 5, 2003 (EST)
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Quote:

1. Should I use my compass purchased here in the eastern U.S. or purchase one locally?

Not a problem. Europe is in Zone 1 for both Silva (Brunton, Nexus in North America) and Suunto (Suunto, Recta, and Silva=Johnson Worldwide Associates in North America). Silva and Suunto have slightly different zoning for the geographic southern latitudes. The reason for the 5 or 6 magnetic zones for compasses (depends on the company) is the dip of the magnetic field, and hence the need to balance the needle or card. You can get "world" compasses that work in all magnetic zones, although they still have problems when you get within about 1000 km of the magnetic poles (northern one is in Elef Ringnes Island at present according to the Canadian geomagnetic website, a bit west of Ellesmere Island).

Quote:

...I have read that a compass bought in North America may not be accurate in South America. Is that a northern vs. southern hemisphere issue or is there more to it, like just being on a different continent?

It is not a question of accuracy, but rather dip. If you are too far away from the geomagnetic latitude that the compass needle or card was balanced for, it will scrape the capsule. Within small limits, you can just tilt the compass in the proper direction and it will work just fine. I sometimes do demos in my Land Nav course with an Australian compass (made by Brunton and looks almost exactly like a similar US model, until you notice the needle is tipped way over). Or just get a compass with a "world" needle. Your North American compass will work just fine in Scandinavia.

Quote:

2. How would I find the magnetic declination in Oslo, Norway? I have had no luck in my searches on the web.

Look on the Canadian (http://www.geolab.nrcan.gc.ca/geomag/mirp_e.shtml ) or US NOAA (http://www.ngdc.noaa.gov/cgi-bin/seg/gmag/fldsnth1.pl) geomagnetic sites. Plug in the latitude and longitude of your intended location and the date, and it will give you the declination (both calculators take into account variation, which is a drift of typically a degree or less per 20 or 30 years).

Quote:

...The reason that I ask before I purchase my topo map there is that I have heard that they sometimes use a system with 400 degrees instead of 360 degrees.

No, no, no. They also have 360 *degrees* in a circle. However, some European maps and compasses give angular measure in *grads*, a metric circle measure devised by the French revolutionaries during their metrification drive following the French Revolution - 100 grads per quadrant (actually it is "gradus" for the singular, as in "degree" for most of the world). Anyway, the map will indicate the declination in grads, if you look at the unit symbol, usually "gr".

6:38 p.m. on February 5, 2003 (EST)
(Guest)

If it is possible to make compasses with a world needle, then why don't they use it in every compass. My Silva Ranger has no global needle but Silva uses it in its Voyager series (and only in its Voyager series). Why not make a Ranger with a global needle ? Commercial reasons ? Accuracy problems ?

10:10 p.m. on February 5, 2003 (EST)
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World compasses

Quote:

If it is possible to make compasses with a world needle, then why don't they use it in every compass. My Silva Ranger has no global needle but Silva uses it in its Voyager series (and only in its Voyager series). Why not make a Ranger with a global needle ? Commercial reasons ? Accuracy problems ?

No accuracy problems. I measure the same accuracy with my global needle compasses as with my zoned compasses. Silva Sweden makes the Voyager and electronic compasses with global needles, although some of the professional compasses (Brunton name on them) have global needles. Suunto was the first to introduce global needles for non-surveyor, non-navigator uses and has a number of global models in the "recreational" lines, including their Recta-branded compasses. Curiously, none of the Johnson Worldwide Associates "Silva" compasses, which are made by Suunto, have global needles, at least none noted in their catalogs. That may be because all Johnson's compasses are sold in North America, hence only zone 1. I do not know for sure, but suspect that Suunto may have some patent or copyright, which has kept Silva Sweden from introducing world compasses any sooner.

Also, orienteering compasses can be special ordered with a global needle (at least the Suuntos can be).

The basic answer to your question is that it is more complex to make a global needle. The global versions of compasses from both Suunto and Silva are more expensive than the "zone" versions, in those cases where there are comparable models.

8:35 p.m. on February 6, 2003 (EST)
(Guest)

Bill S, thank you for the information and the links. Now, off to the snowy north.

September 23, 2014
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