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.

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.