How to Choose a Compass

Choosing a handheld compass for your preferred activity and price range is challenging because of the array of compass types and features.  Any compass that accurately points north could save your life in an emergency, but using the wrong type of compass, and of course, not understanding how to use it, is just as likely to get you into a bind.

You can find plenty of information about different compass types and features at outdoor stores like REI, or from manufacturer websites (Sylva, Suunto, and Brunton are the top brands).  In my opinion, there are only a few compasses that include the right mix of features, affordability, user-friendliness, and light weight for the average backpacker, hiker, camper, birder, hunter, or anyone else using a topographic map and compass for land navigation. Arctic expedition leaders, artillery experts, orienteering race competitors, and people who have a hard time finding their way back to their house each day might have broader compass needs.  Below is my assessment of the essential features that anyone who belongs on the former list should evaluate when buying a compass.

1. Type of Compass

Compasses that attach to your thumb are great if you are running an orienteering course, and the round pocket watch-type compasses look cool, but for most outdoor activities that involve plotting a bearing on a topographic map, a baseplate compass (also called a protractor compass) is ideal.

This type of compass has a rectangular, clear, plastic base that allows you to see past the needle to the map below. The longer the baseplate, the easier it will be to plot accurate directions in the field.  Most baseplate compasses have map scales along the edge of the plate that you can use to measure distances in map units or ground units.  So, if you plan to hike mostly in the U.S., choose one with 1:24,000 scale increments on the baseplate.

Some people prefer to use a lensatic-type compass.  The U.S. military uses these types of compasses, which can be very precise and rugged.  The downside, for outdoor enthusiasts, is the weight, bulk, and slightly more complex compass dial which, if it is one of the high quality models like the Cammenga Model 27, includes Mils as well as azimuth units for direction.

2. Declination Adjustment.

A compass needle points toward Earth’s magnetic north pole, which is different from the geographic North Pole (also called True North)—the point on the Earth’s surface that lines up with its axis of spin.  You can read more about what causes this difference in the magnetic declination post, but the important points to remember are:

• most maps are oriented to true north, not magnetic north,
• declination changes significantly from place to place—as much as 30 degrees!
• it changes a little each year as the magnetic poles wander around.

There are two schools of thought about how to deal with declination.  One argument is that learning how to make a mental declination calculation enables you to use any compass in any situation.  The opposing view favors a compass with a built-in declination adjustment—simply “set” the declination and “forget” about it.

I recommend buying a compass with an adjustable declination option so that you can set and forget the declination each time you head off to a new area to recreate.  You have to remember to reset or at least check the declination each time you change locations by more than a hundred miles or so, but once it is set for that area, your compass will be pointing true north just like your map and you can forget about declination while you are navigating.

Purchasing a compass with a fixed declination scale, rather than an adjustment feature, costs $15-$20 less, but commits you to always having to make a mental (or written) correction for declination.  Lensatic compasses and lower end baseplate compasses do not have adjustable declination features, so my recommendation would be to not buy one of these compasses unless you enjoy making this correction each time you use the compass.

By all means, practice calculating declination in case you need it someday, and to keep your mind agile, but if you are like me, and you think you might have to stop and think carefully about which way to adjust your heading every time you use your compass, go with the adjustable declination feature.  When the unexpected happens and you find yourself tired, cold, and hungry, your bleary eyes and sluggish brain will be able to determine your bearing at a glance…no math required.

3. Needle dip correction

Another weird aspect of Earth’s magnetic field causes the north-pointing part of the compass needle to dip downward into the Earth as you travel closer to the North Magnetic Pole.  In the southern hemisphere the north-pointing end of the needle is pulled upward because the south-pointing end is trying to dip down toward the South Magnetic Pole.

Needle dip can cause a compass to become inaccurate, especially if it severe enough for the needle to scrape the compass housing.  Manufacturers deal with needle dip by dividing the Earth into 5 dip zones.  They sell compasses with magnetic needles balanced for each of these zones.  If you happen to buy a compass in Vermont and take it hiking on the Florida Trail your compass should work fine because both places are within the same zone and the compass you bought probably has a needle balanced for the center of the zone.  If you take the same compass to Tierra del Fuego for a climbing trip, it might not perform as well.

One solution to this problem is to simply test your compass when arriving in a new part of the world to make sure the needle is not dipping so much that it is scraping the compass housing.  If it is, buy a new compass locally before heading into the backcountry.

Another option is to buy a compass with a specially designed needle that works anywhere in the world.  These “global” compasses have recently come way down in price and are excellent options for world travelers.

Military grade lensatic compasses have a deep well design that minimizes needle dip problems—at the expense of bulk.

4. Orienting or Meridian Lines

A series of straight, true north- pointing lines on the bottom of the compass dial housing is an essential feature.  These lines are needed for plotting directions on a map and nearly all the Suunto and Silva baseplate compasses have these.  Some Brunton baseplate compasses have north-south orienting lines in the dial itself.  These smaller lines work the same way, but I would think they would be a little harder to see than lines that appear on the bottom of the housing below the needle (I have not tested the models in question though).

5. Azimuth vs. quadrant compass

Some compasses use the quadrant method for describing directions, while others use the azimuth method (see Compass Directions). The quadrant method, in my opinion, is unnecessarily cumbersome. A direction of South 45° West on a quadrant compass is simply a three digit number—225° degrees on an azimuth scale compass. Going with my philosophy of keeping things as simple as possible in the field, I recommend an azimuth compass.

However, some people might find the quadrant method easier to use with a protractor if they are plotting a lot of bearings on a map.  Other compasses show both quadrant and azimuth scales on nested compass rings.  I think these can be cluttered and lead to mistakes, so I would avoid them.  Manufacturers usually specify the method used in their sales materials and often even in the model name.  Look for the letter Q to indicate a quadrant style compass.

Military lensatic compasses use an additional scale called Mils.  Rather than 360°, the compass dial is divided into 6400 mils.  Each tic mark is 20 mils wide.

6. Mirror

Some baseplate compasses have a flip up mirror.  Rather than holding the compass in front of you and looking down at the needle then up at an object in the distance, the mirror compass is held at eye level so you can sight an object in the distance and watch the needle (looking through the mirror) simultaneously.

Used properly, a mirror compass can be more accurate than a regular baseplate compass. It has the added benefits of extending to make a longer straight edge for plotting directions on a map, and it can be used as a signal mirror in an emergency.  The tradeoffs are slightly higher weight and bulk and, of course, price. If you can swing it, go for the mirror compass.  With practice you will be able to sight objects very accurately, and the mirror is a great safety measure.

The military lensatic compass works very similarly to a mirrored baseplate compass, but as mentioned previously, is a bulkier, heavier, and does not include an adjustable declination feature.

After choosing a compass, be sure to take the time to learn how to use it and practice some before embarking on your epic adventure.  Most manufacturers include basic instructions, and there are several map and compass books and videos available to help you become an expert in no time.