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Suunto M-3 D Declination Adjustable Compass Review

Suunto-M3-Compass Review

The Suunto M-3 D Compass is a baseplate style adventure compass with a declination adjustment that is optimized for use in forested or mountainous terrain where you can rarely see your destination. I’ve been using mine for 10 years, ever since I became really interested in off-trail hiking and navigation and started teaching those skills as an instructor for the Appalachian Mountain Club.

Suunto M-3 D Compass

Ease of Adjustment
Visibility
Stability
Low Light Operation
Durability

Powerful Navigation Tool

The Suunto M-3 D Compass features declination adjustability, a baseplate, and good precision. It is easy to use for navigating and robustly made.

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There are three things that I look for when evaluating a compass for personal use:

  • Does it have a declination adjustment?
  • Is it a baseplate compass?
  • What is the degree of precision on the bezel ring?

Declination Adjustment

A declination adjustment lets you navigate using map north (also called true north), instead of magnetic north. This means that you never have to add or subtract degrees to bearings when translating between the map and a bearing that you want to follow on your compass or from the field to the map. Adding and subtracting declination adjustments is a huge source of confusion and errors, for beginners and experts alike, that goes away with a declination adjustable compass.

Declination Example
The declination is set to 16 W at the base of the dial and the bearing reads 344 degrees when you face north and put red in the shed (the needle points to magnetic north)

With a declination adjusted compass, the needle of your compass still points to magnetic north, but the bearing on your compass bezel is offset using the declination marked on your map, so that the number of degrees that you read off the bezel factors the declination in, without you having to add or subtract degrees in your head.

Your map's declination is usually located near the map scale. This one is 16.5 degrees west.
Your map’s declination is usually located near the map scale. This one’s is 16.5 degrees west.

Let’s say your declination is 16 degrees west (you find this on your map). When you face north and point your compass to magnetic north (put red in the shed), the bearing on your compass will be 344 degrees instead of 360. It actually doesn’t matter what direction you face, because the declination adjusted bearing will always be offset by those 16 degrees west, when you put red in the shed.

Baseplate Style Compasses

The straight edge sides of a baseplate style compass are essential for plotting bearings on a map. Without a straight edge, it very difficult to draw a line between your current location and your destination and read the required bearing off the compass. It just introduces too much undesirable error.

You want a straight edge to draw a line between your starting point and your destination, so you can accurately read off the required bearing.
You want a straight edge to draw a line between your starting point and your destination, so you can accurately read off the required bearing.

It’s very helpful to get a compass with the longest baseplate edges you can find, not just for reading bearings but for marking up your map if it doesn’t have true north lines drawn on it already. Drawing these lines in with a pencil make it easier to align the north-south lines inside your bezel with the north-size lines on your map (shown below.)

Each tick on the Suunto M-3 D Bezel represents two degrees
Each tick on the Suunto M-3 D Bezel represents two degrees

Degree of Precision

The degree of precision or space between the tick marks on the Suunto M-3 D bezel is two degrees, which is more than adequate for navigating on foot. If you’re careful, you can position the bearing mark at the top of the between the tick marks, giving you one degree of precision.  A compass like the Suunto Clipper which has 10-degree increments is completely useless for point-to-point navigation and I wouldn’t recommend using it for that purpose.

Recommendation

I’m a big fan of the Suunto M 3-D Compass because it is easy to use for quick and dirty as well as finely, detailed and calculated hiking navigation. This compass has taken me to some pretty wild places, here and abroad, and never let me down. Declination adjustability, a baseplate, and good precision: those are the key features I look for in any compass, and the Suunto M-3 D delivers.

Disclosure: The author bought this product with his own funds.

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31 comments

  1. Found this great post from the gear in review email that Philip just sent out and tossing in my $.02… I think the MC-2 is more than worth the extra $. In fact I think it is almost the same price or a few dollars more right now on Amazon. Weight & bulk is negated by convenience IMO.

  2. Philip, what is your fav compass these days? Still this model?

  3. I think this is the best explanation of declination adjustment I’ve ever read. I had no idea it made compass navigation so much easier. Thanks! I have to get myself this compass.

  4. Do you ever draw declination lines on your map, like the true North lines? Then you just use those lines and don’t have to fiddle with declination on your compass.

    • Never. You ‘d need a protractor to draw -16.5 degree (or whatever your declination is) lines on a map. I just draw vertical lines that represent true/map north using my compass baseplate. You line it up against the side of the map which is a north/south axis. So much easier and doesn’t require bringing a plastic protractor into the field if you need to do it on the fly.

      Of course, many maps already have vertical grid lines on them and you want to be able to use them too without doing more math.

      • Philip is exactly right on this.
        Drawing in declination lines on your map is a wildly outdated way to use map and compass.
        Just spend a few extra dollars and get a quality compass with adjustable declination.
        I just it once for your local area, and then simply forget about declination, because you measure all bearings to true north.
        The Suunto M3 is one of the best.

        The old school “east is least west is best” backcountry arithmetic might sound easy when you first learn it, but remembering it five years from now when you’re stressed out and lost is going to be very difficult.

    • This is one of the things I teach my Map and Compass students: prepare your map before you go out in the field.

      Since not all compasses have the declination adjust feature, one of the ways I teach my students to prepare their topo map is to add declination lines on the map solves the problem. Sure, the declination adjust feature on some compasses take the guesswork out of adding or subtracting the area declination value but the added declination lines produce the very same results.

  5. This compass is fantastic, I switched from the Suunto A-10 to the M3-G (global) a couple year ago when I started bushwhacking and have been very happy with this reliable tool. The global version is essentially the same but swaps the hemisphere-specific needle for a global needle (just in case I ever go hiking in New Zealand) and adds a clinometer for slope estimations. Adjustable declination alone is worth the upgrade from the A-10, it greatly simplifies map-and-compass navigation.

  6. I have a Suunto A-1, love it for the simplicity and ease of use.

  7. If you adjust the declination on the compass, can you still orient the map by aligning the north/south lines inside the compass capsule with pre-printed “true north” map grid lines ?

    Or do you now have to orient the map by aligning the compass needle with the pre-printed “true north” grid lines ? (Which never seems to be near a grid line…)

    I’m thinking that you have to draw magnetic north grid lines on the map in order to still use the north/south lines inside the capsule to orient the map. And if you have to do that – then I don’t see the benefit of a declination adjustable compass. Am I missing something ?

    Ps: I’ve drawn the magnetic north grid lines onto the map at home. It’s not very hard with a protractor and 2 ft long metal ruler :)

  8. If you adjust the declination on the compass, can you still orient the map by aligning the north/south lines inside the compass capsule with pre-printed “true north” map grid lines ?

    –>yes. the inner capsule lines are still parallel to the baseplate edge and the direction of travel. Only the bezel is offset, so it will read 344 if you have a -16 declination.

    Or do you now have to orient the map by aligning the compass needle with the pre-printed “true north” grid lines ? (Which never seems to be near a grid line…)

    –> no because the compass needle will always point to magnetic north. The offset is made on the bezel only

    –>With a declination adjusted compass, you NEVER need to orient a map. You just read the bearing off the map, stand up, put red in the shed, and walk the bearing. No addition or subtraction required.

    I’m thinking that you have to draw magnetic north grid lines on the map in order to still use the north/south lines inside the capsule to orient the map. And if you have to do that – then I don’t see the benefit of a declination adjustable compass. Am I missing something ?

    –>you don’t *have* to draw those lines. you can simply add and subtract the declination in your head and still use the true north grid lines. Problem is that people always make mistakes. People also don’t draw magnetic declination lines on maps. It’s too much of a pain in the ass and you can’t really do it in the field or on ANY local map someone pulls out of their pocket. Most printed/commercial maps have north south gridlines. Might as well use them.

  9. I recommend you upgrade to the MC-2. The mirror dramatically improves accuracy when taking a bearing on a distant object. The folded out lid almost doubles the length of the baseplate, making it easier to span points on the map. You get a clinometer to measure slopes for avalanche assessment or just knowing how steep that slope you’re climbing is.
    Mine is 30 years old and still works like new. I don’t have too many pieces of gear I can say that about.

    • Seconding this recommendation. I’ve found that being able to fold out the mirror helps immeasurably when plotting on a map.

      • I find the mirror completely worthless in forested terrain where you can’t site on distance landmarks and don’t recommend it for navigation in that kind of terrain.

        • I’m with Philip here. The tiny bit of extra accuracy that you may gain with the mirrored compass is really not worth it for most recreational users. And, depending on your visibility, it may not really help you at all.
          Professional users, like foresters and search and rescue teams might need it.
          But keep in mind, a mirror adds cost, bolk, weight, and is one more moving part that can break.

  10. How do you make the declination adjustment ? Is it with a screw or where you press the center and then try to rotate the declination like on Bruton ( which is very difficult).

  11. I used to like the Brunton Eclipse Adventure Racing Compass with the built-in grid squares. However, they wear off with frequent use. Now my main criteria is which one has the biggest magnifying lens. (The Suunto A-30, if you’re wondering.)

  12. Hello, how easy is it to read this compass at night?

    • very easy if you have a headlamp. You’ll need one anyway if you plan to walk in the dark.

      • If the batteries for my headlamp work, I can just put them in my GPS. The compass is for the Murphy ‘s law case where I have no power. Also, in some cases I like to have my eyes adjust to low light without the interference of a headlamp.

        Is there not enough luminescence to read this compass at night without a lamp or flashlight?

  13. Do you have the Global or Northern Hemisphere version of the Suunto M-3?

  14. Excellent article, concise and to the point! I have one suggestion regarding where to get magnetic declination information. I have a lot of USGS topo maps that I’ve collected over the years and was surprised recently to discover that the information on my 25-year-old maps is way off. It seems that the magnetic north pole has moved quite a bit in that time, so that declination in my area has changed from a couple of degrees EAST to over two degrees WEST. I recommend using a source such as this NOAA site to get the latest information:
    https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml
    Anyway, I just ordered a Suunto M-3 NH, and will be glad finally to have a compass with declination adjustment. I thought surely I could keep it straight and make the necessary correction mentally, but it is so easy to get confused. Even with a minor correction such as the 2.5 degrees in my area, get it backwards and suddenly you’re 5 degrees off.
    Thanks for the great article.
    (By the way, you can use that NOAA site to look at values from any time in the past and see how much declination has changed in any particular area.)

  15. Re night visibility — luminescence is strong on the Suunto compasses, but it fades over course of a couple of hours. If you have a flashlight you can “recharge” quite quickly (2 or 3 minutes). Re M3 v MC2, I’ve never experienced any useable difference in accuracy. Both good instruments. MC2 does give longer baseline and mirror has other uses (signalling, gazing on you own glorious countenance). M3 is more pocketable, simpler, and somehow more intuitive. You won’t go wrong with either one. My one beef with Suunto is the microscopic tinfoil excuse for a “screwdriver” they supply for declination adjustment. Get yourself a tiny eyeglass or jeweler’s screwdriver and chuck that bitty piece of junk!

  16. I have this. It’s nice but a little heavy for ul backpacker at 52 gams. Also needs the lanyard for declination tool and I don’t use the lanyard so it’s just extra. The Brunton TruArc3 is 36 grams and has tool-less adjustment which appeals more to me. I do like having declination adjustment and a lighter similar compass without it saves only around 10 grams so I think it’s worth it.

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