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Compass Use Definitions and Parts

When first learning to use a compass there are a few things to know about the instrument beyond "red points north". Knowing the different parts of a compass and their functions will greatly aid you in using this very old but VERY effective tool when you're on the trail.

Here are some definitions that will make it easier to understand the compass:

• Adjustable compass - A compass whose azimuth circle can be rotated relative to the lubber's line.

• Azimuth circle - A circular compass scale graduated in angular units: degrees, cardinal points, or other units, usually clockwise from north or 0°.

• Bearing - The angular direction to a landmark.

• Boxing mark - A box, arrow, line, or other mark permanently fixed to point to the N or 0° index on a compass azimuth circle. The boxing mark is usually part of the capsule. To "box" a compass, align the compass needle or card with the boxing mark, north-to-north, or with N or 0° on the azimuth circle.

• Capsule - A sealed transparent case which houses the compass needle, the azimuth circle, and the boxing mark. The capsule may be filled with liquid to amp needle or card swinging.

• Card - An azimuth circle mounted on a compass needle. The card rotates relative to the lubber's line.

• Course - Angular direction of travel.

• Fix - The position indicated by the intersection of two or more bearing lines.

• Landmark - A recognizable real object in the terrain around you.

• Lubber's line - Also called a bearing line or direction of travel arrow. A line or mark on the compass body that points toward the direction of travel. Simple compasses may use north or 0º on the azimuth circle as a lubber's line. On sighting compasses the sight centerline is the lubber's line.

• Magnetic declination - Easterly or westerly angular difference between the direction to the earth's geometric and magnetic poles.

• Magnetic inclination - The vertical component of the earth's magnetic field which causes compasses needles to dip.

• Map object - A picture or symbol used on a map to represent a landmark or other object.

• Needle - A magnetized pointer resting on a pivot in the capsule, free to rotate relative to the lubber's line and azimuth circle.

• North - grid north: The direction to the earth's geometric north pole along a meridian.

• North - magnetic north: The apparent direction to the earth's magnetic north pole, not usually indicated by a grid on maps. This net magnetic north comprises all the magnetic effects acting on your compass.

• True north: The direction to the earth's geographic north pole, indicated in life approximately by Polaris; indicated on maps by DMS scales and tick marks along the map borders.

• Orienteering compass - An adjustable compass with special features that make it more convenient to use in the field with maps.

• Orienting lines - Visible lines in the capsule engraved parallel to the boxing mark; used as reference lines when marking angles on the map with an orienting compass.

• Sighting compass - A compass with a mirror or peep sight aligned with the lubber's line.

• Simple compass - A compass with the lubber's line fixed at north or 0°, and a fixed azimuth circle.