Brunton ECLIPSE 8099 Manual De Instrucciones página 4

2 -- Magnetic Declination
The Earth is completely surrounded by a magnetic field, and an unobstructed magnetized object
will orient itself with magnetic north and south poles. Magnetic declination (or magnetic variation) is
the difference between true geographic north (north pole) and magnetic north (in northern Canada),
with respect to your position. It is important to note magnetic declination at your position, because
magnetic declination varies and fluctuate slowly at different rates, around the world (figure 4).
Visit the National Oceanic and Atmospheric Association (NOAA) on the Internet at
www.ngdc.noaa.gov/cgi-bin/seg/gmag/fldsnth1.pl for current magnetic declination values.
Figure 4
ISOGONIC CHART
East Declination ° West Declination
0
4
The isogonic chart shows North America, only. Use an isogonic chart, or a current United States
Geological Survey (USGS), Bureau of Land Management (BLM), or another map to determine
magnetic declination at your position. Declination can be east, west or even 0°, from your current
position. At 0° declination, true north and magnetic north are aligned.
Example: If magnetic declination at your position is 15° east, then
magnetic north is 15° east of true geographic north. Figure 5 displays
true geographic north and magnetic north, as indicated in the legends
of USGS and BLM maps.
Most maps use true north as a reference. When adjustment for mag-
netic declination is complete, a bearing measurement will be with
respect to true north, same as the map.
2.1 Magnetic Declination Adjustment
1. Find the magnetic declination at your current position, from a map or chart.
2. Remove rubber shoe, and open both covers.
3. Position the compass with bottom of clear base facing you (figure 6).
True North
Magnetic North
15 o E
Your Position
Figure 5
Figure 6
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