Understanding Compasses

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By Suunto.

The compass is one of the ten essential gear items found in every hiker's pack. While, for many, the compass rarely makes it out of the pack, it becomes indispensable in foul weather, complex routes, or when you lose your way.

What is the purpose of a compass?

Have you ever been lost on a city street? It is pretty easy to find help and get directions. In the wilderness it is not quite so easy; you need to rely on yourself and your compass. A compass is one of the essential gear items that should always be with you in the wilderness. It will keep you from getting lost, and it will help you find your way once lost. In short, your compass will always tell you where north is, which is not much, but often all you need to find your way. No matter if you are a beginner backpacker or an experienced orienteerswoman, whether you know the trail well or are on it for the first time, you should always have a compass and know how to use it. You might not use it on every hike, but it will be there when you need it.

Compass types.

There are as many compass types as there are outdoor activities; the one that you choose depends on your navigation skills and your activity. If you are embarking on a cross-country route in the backcountry, you need a more sophisticated compass than for a dayhike on a well-traveled and populated path. Ease of use, size, weight and styling will also weigh in your compass selection.

Basic compasses.
- Standard Base plate Compass: simplistic design with strait edges for triangulation and a basic capsule. May include magnifying lens, declination adjustment, luminous components, lanyards and different scales for worldwide use. Ranges in price from $5 to $40.
- Mirrored Base plate Compass: has all of the same features as the standard base plates but with a sighting mirror for greater accuracy while taking visual bearings. Ranges in price from $20 to $80.
- Ergonomic Base plate Compass: a base plate compass with a rounded back edge for a better fit in the hand.
Advanced compasses.
- Wrist Compass: simple compass mounted with a wrist strap for quick general reference.
- Global Compass: an advanced design that allows one to use it any where in the world regardless of the magnetic balance zone.
- Competition Compass: worn on the thumb with map held in the hand; used by experienced orienteering competitors.
Specialized-purpose compasses.
- Lensatic Compass: has an indestructible case built around it; primarily used by the military because of its heavy weight.
- Optical Compass: professional compass used in the forestry field; not designed for use with map.

Technical features.

Features on any basic orienteering compass:

Base plate: transparent, rectangular plastic base for the capsule. The longer the base plate, the easier it is to use for triangulation, and the more accurate your reading.
- Scale lines help you measure distances on your map.
- Direction arrow points toward your objective.
Freely rotating magnetic needle: this needle "floats" in the capsule so that the red end of the needle always points to magnetic north. The two ends of the needle are different colors so that you can remember which end points north.
Rotating capsule for the needle: the capsule is filled with fluid that dampens (reduces) the vibrations of the needle, making readings more accurate.
Bearing System around circumference of housing: the dial should be graduated clockwise in degrees from 0 to 360 in 2 degree increments.
North-South arrow and North-South lines: located beneath the needle, these parallel lines aid in marking your route on a map. Use these lines to align the compass with the N-S lines on your map.
Index line: read your bearings here.

Optional features on some mountaineering compasses:

Adjustable declination: an easy, dependable way to correct for magnetic declination; well worth the added cost.
Sighting mirror: another way to improve accuracy by 30%.
Ruler (calibrated in inches or millimeters): for measuring distances on a map
Clinometer: to measure the angle of a slope or height of object
Magnifying lens: to help read closely spaced contour lines