Declination - Suunto KB Serie Mode D'emploi

The cotangent table at the back of the
compass may be used for distance
calculations and especially for determining
locations when two landmarks appear in a
C
very narrow angle. This situation is depicted
on the same map. In this example the angle
B
between the lighthouse and the sea mark is
D
20°. Assisting line BD is drawn from the
90°
345°
lighthouse advancing along the directional line
325°
20°
of the sea mark. The assisting line is in a 90°
angle towards the directional line of the
A
lighthouse. The segment BD of the line is
measured on the sea card (in this example the
length is 7/8 nautical miles). The distance
between the boat and the lighthouse is then
cot 20° x 7/8 = 2.4 nautical miles on the
directional line AB.

DECLINATION

Declination refers to the measured difference between the magnetic North indicated
by the compass and the North of the map. The local declination is given on the map
margin either as easterly plus declination (E) or as westerly minus declination (W).
The local declination needs to be added to or subtracted from the compass bearing
before the direction is determined using the compass may be read on the map. When
the reading is taken from the map and this bearing is needed on the compass, the
procedure is reversed. Sailors refer to declination as "variation".
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