Home / Gear Reviews / Suunto M-3 D Declination Adjustable Compass

Suunto M-3 D Declination Adjustable Compass

manufactured by:
Philip Werner
Version:
1
Price:
43.00

Reviewed by:
Rating:
5
On November 20, 2015
Last modified:November 20, 2015

Summary:

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 delivers.

Suunto M3 Compass
Suunto M-3 D Compass

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 4 years, ever since I became really interested in off-trail hiking and navigation and started teaching those skills as a instructor for the Appalachian Mountain Club.

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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13 comments

  1. 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.

  2. 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.

  3. 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.

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

  5. 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 :)

  6. 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.

  7. 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.

  8. 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.

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