Brunton 7DNL Compass Review

[Rog Tallbloke]

The Nemonics I learned were MUGS and GUMA. Map Unto Ground – Subtract, which seems opposite to your first man adam aide memoire. I guerss it depends whether you regard a westerly deviation as positive or negative number.

[Roger Caffin]

> I guess it depends whether you regard a westerly deviation as positive or negative number.

Does it also depend on what the local deviation is? Positive or negative?

Cheers

[Nicholas Luhr]

>Does it also depend on what the local deviation is? >Positive or negative?

These kinds of questions are EXACTLY why you should have adjustable declination. When you get lost and you're already running on the amygdala and not the cerebrum, you don't want to depend on questionable mnemonics and potentially careless arithmetic.

Anybody can work it out on paper sitting at the dining room table but when you're wet cold and lost, and you are getting narrowed focus and less ability to process additional stimuli, you DO MAKE MISTAKES.

[Chris Townsend]

It's easy enough to mark declination on a compass with a piece of tape, not that I've ever done this as I don't think it's necessary. Plenty of non-sighting compasses have adjustable declination if you want it though I don't think it's essential.

[Tohru Ohnuki]

For my basher compass that i take on local hikes, i marked it already with the mag dec for my area:

[Steve WYSTRACH]

My experience is that the type of compass you need is based on the type of navigation you expect to do, plus experience. Personally, I’ve never used the mirror-sighting type on an outing, although they are great for easily taking accurate bearings. On the other hand, I’ve used a conventional ship’s compass to take bearings, and triangulate position, routinely on sailboats – just sighting over the needle to the lighthouse or smokestack.

As for hiking, I’ve walked several thousand miles on the great web of trails in Europe, with only the tiniest of modern compasses. On my first trip, I needed no more than the little button compass that was embedded in my REI trekking poles. It decayed and froze up during the first month. (Incidentally, afterwards, REI told me it wasn’t intended for navigation – hmmn, I thought). Fortunately, I reached Limoges, France, just as that occurred, where I purchased a Recta Clipper compass. It’s sold as the Silva Clipper in the US.

For trail work, with occasional distant bearings, the odd cross-country “short cut”, etc. (with a topo map as Roger says), for 10 bucks and 5.9 grams, it’s pretty hard to beat. It’s been my http://www.longwalking.com compass of choice, still bubble free, for the past 6 years.

So it all just depends on the outing. Thanks, Roger.
Cheers! I hope to see you on the trail. SM

[David Corbin]

Roger wrote: "I have to tilt the compass slightly (about 5 degrees) to be absolutely sure the needle is able to swing freely . . . The need for this tilt is hardly surprising, as the magnetic field around where I live (Sydney, Australia) is actually tilted some 64 degrees downwards. That's really pretty savage . . . all our compasses need a similar amount of tilt to swing most freely"

The reason Roger has to tilt his compass is because the vertical intensity and direction of the earth's magnetic field, the inclination, influences the horizontal plane of a compass needle according to the latitude where it is used.

Some compasses, such as the Suunto M-3G Global, have a "Global Balancing System," which helps keep the needle horizontal at different latitudes.

Two other important characteristics to look for is 1) how quickly the needle centers; 2) how free from wobble the needle is; 3) luminous markings. Also, a jewel bearing may desirable for consistent performance over the years.

[john flanagan]

I'm solidly with the "fancy stuff is fun extra weight but not critical" camp on this one.

Errors in declination settings are easily avoided by scribing Mag North/South lines across the map. Take bearings by aligning the N/S lines in the compass housing with those instead of the longitude lines that form the edges of the map. No math or mneumonics to decide whether to add or subtract declination required.

I've not yet found errors in sighting without a mirror to be an issue in practice. The fact that mirrored sighting compasses are accurate does not prove that simple base plates are not, assuming careful and skilled use. I suppose that the flip side is the fact that I've never had an issue with it doesn't mean that I never will…

Accurate navigation without GPS rests mostly on continuously tracking your position on the map using terrain and other features. Trying to find your position after having the map in your pack for an hour is exponentially harder.

Generally, in my experience the compass comes out mostly in low/no visability situations. Ideally in those situations, you navigate with deliberate error planned in. This means rather than shooting for a single pinpoint on the map, you shoot for catch lines, such as ridges, streams, or given an altimeter, even approximate lines of altitude. A deliberate error (aiming off) of a few degrees ensures that you know whether to turn right or left at your catch line.

When there are no catchlines (eg flat terraine, all bog/no stream or northern forest with kettle ponds, sailing to an offshore bouy in the fog) and there is a critical point to find – the GPS is the best dang thing since sliced bread.

Otherwise, leapfrog navigation works well. This means sending a party member out to the edge of hearing and visability and moving them left or right to align them accurately with your bearing. This is probably the best scenario to argue for precise accuracy, but using a mirror to sight is slow and again, careful use of the base plate accurate enough.

In my view this is one of those recurring topics that has clearly divided camps. The fun is in the arguement – no harm done by adapting either stance or piece of gear. I've not yet heard of a serious mishap in the mountains that was rooted in the kind of compass the victim used. Lack of skill and knowledge…failure to have…failure to use… yes, yes and yes. Having one kind of compass instead of another? No.

[Rod Lawlor]

"I can travel over a mile through dense hilly/rocky/forest and streams and come out with an accuracy of less than a half degree error from my starting point because I am able to sight with tight accuracy on objects that are relatively close to me (distant objects being blocked from view) and continue following my bearing with accuracy and precision. That is within 46ft over a mile of difficult travel (clambering over rocks, downed trees, around brushpiles, through streams, etc. How close can you get without a sighting mirror?"

Bloody hell, if I was only that good, my rogaining partner would sack me. He expects 5m (16ft) accuracy over 4km (2.5miles) If we don't walk straight on to a checkpoint, through pretty dense bush, at night, after 14hrs of competition, we're wasting time.

As Roger says, we're using a compass (baseplate) for general direction, but primarily running to the map. If we're traveling fast one of us will read the map, and the other one will read the ground.

I do like declination adjustment though. It's faster, and saves screwups at 3am.

[Joshua Gilbert]

+1 on the idea that mirrors, declination adjustment, and clinometers are fun but not needed.

I took a wilderness navigation course with the Seattle mountaineers last fall, just to brush up on some skills and to actually get some formal training for once. They required that your compass have adjustable declination, so I had to buy a suunto mc8 (or something, can't recall right now; a baseplate compass w/no sighting mirror) as my old Silva sighting compass didn't have declination adjustment (just the red numbers inside the housing)

I found it pretty easy to travel overland using a baseplate compass w/no mirror, and I came out just about dead on (maybe 1/2 a degree over 1 mile, I was about 3 feet away from the marker) I know experienced orienteers do better, faster and with less.

I've done more complex stuff with a mirror, but I was less experienced then as well.

Nothing wrong with any extras on a compass, they are fun to play with, but saying you must have them is a little excessive I think.

[Roger Caffin]

Hi Rod

> He expects 5m (16ft) accuracy over 4km (2.5miles)

Way back … in Boy Scout days … we were set a navigation exercise. In brief: we were allowed to study the map for a 3 km trip for about 10 minutes. We were told our start and end positions. Then both the map and the compass were taken away.

So we had to navigate using terrain and the stars. Oh yes – I forgot to mention: this was done at night! No sun, no visibility. Use the stars to determine the South Pole.

I was half way there when I realised I had not allowed for the 11 degrees of magnetic declination … Ah … right. Alter course by about 22 degrees and set off again.

But we could cheat near the end, because we could smell the sausages being cooked for our dinner. Despite the error I was within 50 m. Yeah, we all got dinner.

Cheers

[Tohru Ohnuki]

This is way off topic now, but here's a dorky exercise: Using a GPS as a compass. If you want to get a good prelim bearing on a tower for a microwave path, you can't use a compass anywhere near it because the steel structure will mess up the magnetic field. So get a GPS fix at the base of the tower, walk out a hundred yards or so and then use goto to the base waypoint. Walk back and forth until you get a good estimate of the bearing (it's a reverse bearing actually.) Put a flagged stake there, and then repeat the process another 100 yards out. This works pretty well and of course the final aiming is done by maxing the signal strength…

[Roger Caffin]

> the steel structure will mess up the magnetic field
The steel structure may also upset the GPS signals, under some conditions.

Cheers

[Bob Gross]

"The steel structure may also upset the GPS signals, under some conditions."

I could not agree any more. I've been responsible for thousands of GPS antenna installations, and a percentage of them have been on, in, or around steel towers. The tower can directly block GPS reception in some cases. More often, the flat steel surfaces cause multipath interference. So, if you have an extremely expensive choke-ring GPS antenna, you can keep working. If you have a simple portable GPS receiver… forget about it.

Further, during a storm, the steel tower tends to act like a lightning rod, so that is the last place where I want to be.

–B.G.–

[Paul Davis]

Thanks to Roger for a great review!

I admit that I often leave a Suunto MC2-G compass at home and rely on the one in my Doug Ritter survival kit—a quality 'button compass'.

Having said that, there are some advantages to using a sighting compass with a mirror in the Canadian North.

First of all, the declination here can vary enormously withing a 1 hour flight time of here, so dialing it in on a fixed scale with the metal-tooth-pick-style declination screwdriver on the compass lanyard avoids much accidental idiocy.

The 'G' series Suunto compasses have a 3D gymballed needle that is truly global in terms of magnetic flux; it will continue to float freely up to about 20° off of the horizontal. This is also useful to those of us who have a hand tremor or are otherwise horizontal-levelling challenged. It will also function closer to the magnetic pole than most compasses which peg-out when confronted with downward-angled magnetic force lines…

Sighting mirrors are still useful, as off the tiny Northern road network we really do still triangulate from known points, do a 'cocked hat' of 3 bearings, to fix our position. We also signal aircraft with the mirror, or discover how shocking we look before heading into town…

The MC-2G, or for that matter the Brunton-Silva Type 15 Ranger, have compass bezels with lugs on them big enough to be used whilst wearing contact gloves or mittens, and are luminous enough to be useful in subarctic darkness.

Oddly enough, I find the opaque cover of the sighting mirror to be an ideal place to epoxy a velcro patch, such that the compass hangs on a velcro patch on my left pack strap, attached by its lanyard against loss, so no strap-around-neck issues! I don't know how I could do this with a baseplate compass without a mirror cover!

Compass bubble issues are not that difficult to solve—Silva cheerfully replaced my 'capsule' after far too many Canada-Africa aircraft flights which led to bubble development, so 're-capsule' before replacing a compass! My Silva 15 Ranger survived 30 years of service, and is on its 2nd capsule, now serving another user in The Pas, Manitoba…

Here, we use the clinometer for risk evaluation for avalanches by checking slope angles.

Thanks again to Roger for a great review, and to all of you for interesting comments!

[Rog Tallbloke]

>I guess it depends whether you regard a westerly deviation as positive or negative number.

>Does it also depend on what the local deviation is? Positive or negative?

Well it's either going to be westerly or easterly. Unless it's zero.

I find it easiest to visualize the problem rather than rely on mnemonics myself. If the deviation is westerly, and I'm heading north, then if I set the compass to the map gridlines, I'll end up walking west of north. Therefore, I need to add the deviation to the bearing to end up going north.

[Roger Caffin]

Hi paul

Thanks for the comments. Just one thing:

> dialing it in on a fixed scale with the metal-tooth-pick-style declination screwdriver
I'm not familiar with this at all, at least on baseplate compasses. Hum?

With the Brunton I set the declination using the red ring and the gradation under it, and then line up the needle with the lines/arrows on the rotating bit; then the base plate is True North.

Cheers

[Tohru Ohnuki]

These two compasses are doing the same thing, albeit in slightly different ways:

The one on the left is a fixed dec, the one on the right an adjustable dec. The point is that you preset the mag dec on the adjustable beforehand and then line up the needle to the adjusted marks, in this case, the yellow fluorescent lines. On the fixed dec, you have to line up the needle to the dec scale each time.

The sharp eyed may notice a few other things:
1) The compasses are doing the same thing as the north mark on the map, this is a quick check that your compass is set up correctly for your region.
2) The bubble is deflecting the left compass's needle slightly and the right compass's marks don't line up due to the camera not being exactly above it (a problem that is solved when using the sighting mirror.
3) You can't get two compasses this close without them interfering with each other, what you don't see in the photo is the 5 minutes it took lining them up.

[Rod Lawlor]

Suunto MC-2G Global Compass is currently on sale at theclymb.com for $40, until Fri 9am I've never used the site, but am registered there. It's members only, but you can use this link

http://www.theclymb.com/invite-from/RodLawlor

to skip past the registration process. (Be aware that this will credit me with $10 for anyone who makes a purchase. I'm not sure how this will work, since they only ship within the US)

Roger, I realise this should be in Gear Deals, but it seemed relevant here. I'm happy to remove it when I get home tonight if you'd prefer, or for you do so.

Rod

---

Relevant.
Cheers

[Roger Caffin]

Hi Tohru

The compass on the left is pretty much a generic design – available under most brands with minor variations in colour and trim. The bezel on it CAN rotate and be set for declination. There is a white line under the N symbol which serves as the marker when you rotate the dial.

The Brunton 7DNL is essentially the same. The bezel rotates to set the declination. The blue line points to the marker. You line up the needle with the lines on the rotating bezel.

If the bezel on such a compass does not rotate, it is because it is jammed. Sand, dirt etc.

Cheers

[Tohru Ohnuki]

RIght, the baseplate can be set such that you are compensating for mag dec as in your picture. But this means that the baseplate is set to true north only. This is fine if all you want is to orient your map to true north.

The purpose of the dec scale on your fixed dec compass or the adjustable dec is so that the _capsule_ of the compass is set to true north and the _baseplate_ can be set to an arbitrary bearing.

This is so that if you see a mountain off in the distance you line up the baseplate to the mountain, and the capsule to north to get the bearing, which is indicated by the white line you pointed out. Then you can transfer that to your map. Or vice versa, see:
link to Silva 123

[Roger Caffin]

Hi Tohru

> all you want is to orient your map to true north.
Describes me perfectly. In fact, my wife insists that we do that FIRST, every time.

Then we sight over the map to any peak. Works great for us.

Cheers

[Kenneth Linden]

Hi Tohru,
Being a southern California hiker, I couldn’t help noticing that the map you set the two compasses on in the picture above is out of date with respect to the magnetic declination shown on the map. For the San Gabriel Mountains, the magnetic declination is now 12.5 degrees, rather than 13.3 degrees as listed on the map, a difference of almost a degree http://www.ngdc.noaa.gov/geomagmodels/struts/calcDeclination. The declination changes a little year over year.
Having said this, I realize from the above Forum posts, that one group, the baseplate compass group, will be gnashing their teeth at the over-exactingness of it, while the other group, the sighting mirror camp, will take it as a matter of course that one would correct for the current declination adjustment.
Personally, hiking in the San Gabriels and other major mountain ranges in So. Cal., I don’t believe I have ever needed to take my compass out of its case to navigate. The land forms are distinctive enough that I just use the topo map and compare it to the landforms, with the sun as compass enough. The only times I have used the compass is to identify some peak on the distant horizon for interest’s sake by later at home using the bearing and Google Earth (most of these peaks of interest would be off the edges of my topo map). For the record, I use a sighting mirror compass, the Suunto MC-2. I like the clear baseplate, the ability to adjust the declination, the clinometer for avalanche considerations, and I like the idea of carrying a mirror anyway for the reasons mentioned above.

[Tohru Ohnuki]

Hi Kenneth, yeah, it's a Tom Harrison map of the Angeles and you can't easily see it but it does say 2007 mean declination. In point of fact, these compasses aren't better than a couple of degrees accuracy anyway. To do better you would need to break out the surveying tools or a Brunton Pocket Transit, and that's not exactly ultralight. Not to mention having to worry about local magnetic anomalies.

I've never needed to know more than vaguely where north is while hiking here locally either, the sun and the time does a reasonable job at that. If you're paying attention to where you're going and where that is on the map, then like Roger said, you only really need the compass to orient the map.

But in other terrain that's featureless or where landmarks can become obscured by fog, sand or trees, a compass would be much more useful. It's good to occasionally do the exercise of getting a fix on your location by triangulation. For that, an adjustable dec makes it easier.

[Paul Davis]

Roger: I think the declination thing was answered with the excellent photo above—thanks all—both the Suunto MC-2G and the Silva or Brunton Type 15 (Ranger) compasses have a separate clear baseplate which can be swung around by means of a tiny rack and pinion gear, accessed by a tooth-pick style screwdriver on the lanyard, such that even the terminally-tired cannot screw up the declination…works like a charm!

My delay in responding is partially because I have just carpooled 500km N. of here at 64N Tombstone Terretorial Park on a wildlife-watching tour.

Anyways, not being the trip leader, and being sleepy, I left my survival kit in my tent, and did not (gulp!) bring the Suunto with me. +5C rain, fog, 2000M above sea level, lowering clouds.

Group leaders wanted to go up, did not perceive the visibility lowering, though I pointed it out.

Ended up lingering for lunch lower down with a botanist, saw the hikers higher up get swallowed by the clouds, so laid out the bright yellow foam sitz-pad, blew the whistle, and they vectored themselves in by sound.

None had a compass, nor a GPS, none had taken a back-up bearing on the micro-wave relay tower road which was our jumping-off point. This is a trail-less, featureless tundre landscape.

I had a GPS and an Iridium Satphone, so I used the GPS to generate a back-up bearing to get us back to the tower, once they got back to me, as I was below the cloud level.

Memo to self: 'No group hikes without carrying Suunto'!! Even if I am not leading!

Yes, this is why we carry them: dial the declination in, take an insurance bearing with the mirror on your start point, close the lid, and if the fog comes down, open the lid, put the N needle in the S end to create a reciprocal (go home) bearing, use the mirror to choose a bearing marker, even use a hiker 'no, bit to the left, good, stop!', then hike to them, repeat as neccessary…

Get out on the land!

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