Brunton 7DNL Compass Review

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.

>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.

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

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.

"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.

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

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

Cheers

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!

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

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

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

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.

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!