How To: Buy a Compass

Learn the ins and outs of buying a good compass.
The Mountaineers The Mountaineers
February 25, 2014

We get a lot of questions about compasses - and rightfully so! They're important. Follow our directions below to select the compass that’s best for your needs. We suggest that you print this page and take it with you to the store when purchasing a compass.

All compasses have a magnetized needle that points north, and have a way to indicate direction of travel. Mountaineering requires a compass with additional qualities. Compasses that hang from parka zippers or hook on watchbands are not suitable for most of our courses or as part of your ten essentials. 

REQUIRED FEATURES OF  A COMPASS FOR BASIC NAVIGATION COURSE SEATTLE MOUNTAINEERS

1. Adjustable declination: A moveable orienting arrow, which provides a built-in declination adjustment. If there is one feature that simplifies map and compass work, this is it. Compasses with adjustable declination can often be identified by the presence of an adjustment screw, usually brass or copper-colored, and a small key attached to the lanyard.

  • All students MUST have a compass with adjustable declination. The presence of a declination scale does not guarantee that it can be adjusted.
  • If you already have a compass without adjustable declination, you may not use it in this course. Recent experience indicates that such compasses detract from the learning experience.

2. A transparent rectangular base plate with a direction of travel arrow or a sighting mirror.

  •  Transparency allows map features to be seen underneath the compass.
  • The rectangular shape provides straight edges and square angles for plotting and triangulating on the map.

3. A bezel (the rotating housing) marked clockwise from 0 to 360 degrees in increments of two degrees or less. In  general, bezels should be large to allow use while wearing gloves - the larger size also improves accuracy.

4. Meridian lines: Parallel 'meridian lines' on the bottom of the interior of the circular compass housing rotate with the bezel when it is turned. The meridian lines run parallel to the north-south axis of the bezel, however turned. Meridian lines are necessary for plotting and triangulating on the map.

5. A ruler and/or gradient scale engraved on one or more of the straight edges, used for measuring distances. Compasses with other additional scales facilitate advanced navigation.

6. A 3 to 4-inch base plate. A longer straight edge makes map work easier.

Additional recommendations:

  • A sighting mirror in the cover: This reduces errors introduced when moving the compass from eye-level after sighting to waist-level for reading the dial.
  • A liquid-filled housing to reduce erratic needle movement (only needed on some compasses). In some cases, steadying the compass needle can be difficult.
  • An inclinometer: a gravity driven arrow that allows you to measure slope angle.

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Brian Starlin
Brian Starlin says:
Thu, Oct 15, 2015 4:49 PM

As of 2016, the Mountaineers Navigation Course is called "Wilderness Navigation," and these compass requirements still apply.
For #5. SCALE -- Scales of 1:24,000 are preferred over 1:25,000

Additional Recommendations:
Brunton's current models (2015) use a tool-less declination that requires pressing down on the bezel. This can be difficult and cause the pieces to separate. Generally, however, the Brunton's meet our specifications.
Suunto's M3 and MC-2 continue to show a 2-5 degree magnetic error in many instances. Most can be corrected by adding another 2-5 degrees East declination (i.e.. 18 East instead of 16 East). The 2015 model has shorter meridian lines.
Beware of the "UST" compass available online via Amazon and other outlets. Our gear tests show it to be wholly unreliable. -- Brian Starlin, Navigation Committee Co-Chair

Brian Starlin
Brian Starlin says:
Sun, Jan 17, 2016 5:26 PM

Seattle Navigation Committee update for "Compass Requirements for the Wilderness Navigation Course" dated September 2015 -- http://www.mountaineers.org/about/branches-committees/seattle-branch/committees/seattle-navigation-committee/files/required-compass-features-for-wilderness-navigation-2015-2016

Brian Starlin
Brian Starlin says:
Tue, Aug 23, 2016 12:49 PM

As of mid-2016, Suunto has corrected the accuracy issues in their MC-2 compass, and it is once again recommended for Wilderness Navigation use.

Brian Starlin
Brian Starlin says:
Tue, Oct 17, 2017 12:45 PM

For 2017 and 2018, the Seattle Navigation Committee has an updated Compass Requirements document at this URL...
https://www.mountaineers.org/about/branches-committees/seattle-branch/committees/seattle-navigation-committee/files/mountaineers-approved-compass/view
Brian Starlin, Seattle Navigation Chair