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Magnetic declination
Like most compasses, the Trelock Geo Coach is
orientated to the magnetic North Pole. In contrast,
every measurement on a map is always orientated
to true north.
The magnetic North Pole deviates slightly from
the actual North Pole (true north). The angular
difference between magnetic north and true north
is called “magnetic declination”. Its value (degrees
and minutes) and its direction (east or west) de-
pends on where on the globe you happen to be.
You can find the magnetic declination of the most
important cities in the table on P. 36. Other cities
can be found at:
http://www.geolab.nrcan.gc.ca/geomag/e_cgrf
http://www.ngdc.noaa.gov/cgi-bin/seg/gmag/
fldsnth1.pl.html
Compensation of magnetic declination
For more precise navigation the compass must
be adjusted to the magnetic declination. For this
the western (W) magnetic declination must be
Example 1:
23° western magnetic declination and
323° bearing are shown.
actual bearing = measured bearing – western
declination
actual bearing = 323 – 23 = 300°
Example 2:
22° eastern magnetic declination and
278° bearing are shown.
actual bearing = measured b eastern
magnetic declination
actual bearing
= 278 + 22 = 300°
Calibration of the compass
The watch’s compass must be calibrated when
the watch is used the first time
the battery has been changed
the numerals of the bearing flash and the
display ”CAL OFF” appears
the compass is used at a location that deviates
from where the compass was last calibrated.
TRE_GA_GC350-400.indd 74
22.12.2006 11:59:13 Uhr
