Silva SightMaster User Manual page 3

SILVA Sight Master Series is the type of compass
to choose if you depend upon the highest possible
accuracy obtainable with a hand-held magnetic
compass. Typical users of this kind of precision
sighting compass are: Engineers, Surveyors,
Geologists, Foresters, Architects, Military forces,
Marine navigation personnel and others who put
extreme accuracy first.
Instructions for use, PICTURE A and B
1. Hold the compass close to one of your eyes
horizontally in front of you.
2. Sight with both eyes towards the object. See fig. A
3. At the same time as you read the bearing through
the compass sighting system you sight above the
instrument towards the object. The index line will
appear to "stand up" from the compass housing
making it easy to accurately read the correct
bearing towards the object. See fig. B
4. The bigger scale gives the bearing from your
position to the object and the smaller one the
reverse bearing from the object to your position.
Reverse bearings are essential in accurate
positioning tasks, particularly at sea.
Direct reading of bearing
The scale readable from above by the lubber line is
used when following a certain direction in the terrain
or when using the instrument as auxiliary compass
in a boat. Please note that highest accuracy is always
obtained by using the optical sighting system.
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Important!
Some people who have an eye condition called
heterophoria (misalignment of the eye axis) may get
incorrect bearings when reading the compass with
both eyes open. This can be checked as follows:
Take a bearing to the object with both eyes open.
Then close the other eye, and if the bearing does
not change significantly, there is no heterophoria and
bearings can thus be taken with both eyes open.
When there is a difference in the bearings, then
keep the other eye closed and sight partly over the
instrument housing.
PICTURE C
Plotting locations
Aim at two fixed points appearing on the chart, for
ex. lighthouse in direction 20° and landmark in 330°.
Then draw straight lines along the reverse bearings of
20° and 330° (200° and 150°) from the lighthouse and
landmark on the chart. The intersection point of these
bearing lines indicates your location. See fig. C
Declination
The difference between geographical north (towards
which the maps meridians are directed) and the
magnetic north (towards which the compass is
pointing) is called declination (or variation). Declination
changes with location and the local declination is
printed on the maps. Bearing obtained with the
compass should thus be corrected with the local
declination.
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