Needle Compass
 Most
compasses are needle compasses, using a magnetized needle that
align with the earth's magnetic field. Needle housings are
often field with liquid that stabilizes the erratic movement
of the needle, making precise reading possible.
Basic needle compasses are a good choice for beginning adventurers,
day hikers, and backpackers who stick to the trails.
If you travel off trails or deep into the backcountry, look at
advanced models. These compasses will have features such
as sighting mirror, declination adjustment, map scales, Magnifying
lens and more.
Compass features
Bezel Degree Intervals: Most compasses have rotating outer
ring called "bezel", with degree marks from 0°-360°.
For both basic and specialized models, the smaller the interval
of degrees on the bezel, the more accurate your bearings will be
Global Needle: Useful to adventurer
who explore in the southern hemisphere. Due to variances
in the earth's magnetic field, a needle compass designed to spin
freely in North America may tilt or drag on other parts of the
world. Compasses with global needles compensate for these variances
and spin freely and accurately anywhere on the globe.
Sighting mirror: A mirror improves
your ability to make more precise reading. When the mirror
is partially fold open, you can sight through a notch in the top.
This allows you to simultaneously see your bearing and sight on
a distant landmark. It also act as an emergency signaling
device.
Declination Adjustment: A compass
needle points to magnetic north, not true north. This difference
is known as "magnetic declination". An adjustable
declination arrow let you preset this value, which simplifies
navigation. Some Compasses feature a fixed declination "scale"
in their base plates, which allows you to make a quick adjustments.
Tool-free declination adjustment makes the process easier when
you are on the go.
Clinometer: Found on some compasses,
it measure vertical angles and is used to determine slopes steepness
or the height of an object- a tall tree or a building.
Ruler: Used in conjunction
with map scales, it enables you to quickly calculate distance.
Map Scales: Used to calculate distances
on maps, making navigation a little faster. Most U. S. Geological
survey maps use a 1:24,000 ratio, measuring 1 unit on the map
equals 24,000 units on the ground. For example 1" =
24,000" , or 2000' or approximately 3/8 of mile. At
1:100,000, which less topographic detail, 1" = 100,000",
or 8333'. about 1.5 miles.
Liquid Filled: In the needle
housing, a non freezing liquid is often used. The liquid
slows a needle's jiggling and brings to rest quicker than an air-field
housing. At high elevations or in cold temperatures, the
liquid may contract and create a bubble. A bubble will not
impact accuracy. Bubbles disappear when a compass returned
to normal conditions. Other Features: If you often
travel at night, luminous cardinal points ( north south east,
west) or a luminous bezel are beneficial. A Lanyard (or
wrist band) tethers the compass to your wrist; a must for adventure
racing or orienteering. A magnifying lens can help you discern
map details more easily. |
