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Miles, geological compass you have there.

I have used the Suunto and Brunton compasses a lot. Suunto is easier to carry and heck of a lot cheaper.

Some compasses are universal, some area specific due to magnetic declination.

A good GPS will generally work just about anywhere, e.g. Garmin 62 CSx Used mine all over the place, from steep jungle valleys to open African country. Sat phones are another matter entirely!

Adjustable Declination;

If used in conjunction with a topo map it is quite useful, here in SW oregon magnetic north is approx. 19 degrees off of grid north.

On the other hand in Wisconsin for example magnetic and grid north are the same (i.e.. declination is 0 degrees).

If you are just shooting bearings to say find your start point or camp… you would not need it.

Jerry

I don't see any real change in quality between good compasses now and previously. You do have to be careful to get a good model.

I do think the newer adjustable declination compasses that use a tight friction fit are less prone to fail suddenly than the older system with a tightening screw.

I prefer the flat clear base models, with grid alignment lines, that allow use as an on map protractor for general use.

While I have a military lensatic and several with the mirrors, I find for almost all land navigation use that a careful center hold gives me all the accuracy I need when taking bearings.

For most purposes a non adjustable does just fine. That being said, the compasses I actually use most all have adjustable declination. The exception are a couple of small Silvas that weigh practically nothing and pack into a pocket easily.

The model I seem to use the most is a medium sized flat Brunton, adjustable declination, rounded ends that make it slide in and out of pockets and pouches easily (no sharp corner to snag or hang up) with inch and cm scale that makes it easy to use with metric or inch standard maps.

In much of the world, including much of the US, not knowing how to adjust for declination can get you very lost.

I appreciate what its for, but I have always achieved the same thing with a little mental arithmetic...

I am no expert, but from my studies of navigation and compass use, declination is the bending/deflection of the magnetic field lines extending from the poles. In the US, it apparently is minimal near the Mississippi River but varies continuously (and sometimes unpredictably) as you move across the country east(+) or west(-) It also appears to be undergoing a gradual change over time.

My understanding is that declination only applies for bearings taken from the map and applied to the field--not for field bearings taken and used in the field.

According to my favorite book on the subject, "Be Expert with Map and Compass" (by Bjorn Kjellstrom, who is widely referenced by other authors), when navigating from a map to the field as a 1 degree error can put you off by 1/60 of the distance traveled per degree of declination. In Az, at the eastern border the declination is about -11 degrees, and at the western border it is about -13 degrees.

Doing the math, assuming (that I can do the math correctly ?) and that you walked out 5280 feet from a camp at the eastern border of AZ, the -11 degrees declination would result in an error of about 968 feet (5280feet x 1/60 x 11 degrees).

I started with and prefer the old Silva's but lately have been using my Brunton Eclipse compass set up for GPS use, almost exclusively.
Using UTM's coordinates from my GPS, I can plot my position on a topo within a few feet/meters.I am old school when it comes to using the topo maps.
My old Silva's are both Ranger models. When in the field, I wear the smaller one around my neck pretty much all the time. I believe they are really good when used for field travel as you can easily sight landmarks and maintain a heading, but not as good as the Brunton for map work.

I have read the bubbles come from changes in atmospheric pressure ie--altitude, and as long as they don't interfere with the needle movement, they don't hurt anything. I believe this is true as my Silva's have bubbles at altitude but they go away when back in Phoenix.

Good luck.
Joe

"My understanding is that declination only applies for bearings taken from the map and applied to the field"

This is true or vice versa and what I was trying to say above.

"not for field bearings taken and used in the field."

This is also true, if you only use your compass to shoot a bearing as you move out into the field, you can use the reverse of the bearing(s) to make it back to your camp (basically you are making your own map)… Declination does not matter.

I won't buy a compass without adjustable declination as inevitably I will use it in conjunction with a topo map.

If you get a chance take a look at a compass that is in quads. the compass face is divided into 4 quadrants; starting at North and moving clockwise they are NE, SE, SW & NW. Hard to explain so refer to the picture, each quad starts in either the North or south at zero and goes to 90 degrees to either the east or west. What is slick about a compass in quads is that if you are traveling say N47E, then the reverse of that azimuth would be S47W. They are super easy and fast to figure your back azimuth. You of course can do the same with a 360 degree compass by subtracting 180 degrees, I just find the Quad compass faster and easier to work with.

Jerry

Well that's not a problem, it's just a minor convenience,to be able to set it for the trip.

Thr primary cause of declination is simply the physical location of the magnetic pole. Only if you are directly south of it (in simple terms) will your compass readings be declination free.

The magnetic pole is moving, and it's movement rate is accelerating. Might be Bush's fault...

Also, if you are using the compass in quite different areas, e.g. low to high latitudes, look at a universal balanced compass to avoid problems with the "dip" of the needle causing binding on the compass.

I have no idea how they make those, but for a traveller, they are well worth it..Some company's also refer to them as a "global" compass...

I used many compasses in my work, owned a Recta and it developed a bubble so I gave it away.

I bought a Leupold Sportsman in spring, 1969 and while heavy and slow, it always works, is robust and is always in my emerg. kit in my pack. I will never replace it and trust it in any conditions.