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Computing Azimuths
Since azimuths are easier to work with, most surveys prefer them. Azimuths
calculations are best made with the aid of sketches. But before azimuths or
bearings are computed, it is important to check that the figure is geometrically
closed: (n-2)*180.
N.B: If the computation is proceeding in C.C.W manner, add the interior angle
to the back azimuth of the previously course.
If the computation is proceeding in C.W manner, subtract the interior angle
from the back azimuth of the previous course.

2.5 Compass Survey
A compass consists of a magnetic steel needle mounted on a pivot at the center
of a graduated circle. The needle aligns itself with the earth’s magnetic field.
Magnetic declination is the horizontal angle from the true geographic
meridians to the magnetic meridian. An east declination exists if the magnetic
meridian is east of true north; a west declination occurs if it is west of true north.
Because the magnetic pole positions are constantly changing, magnetic
declinations at all locations also undergo continual changes. For any given time,
the declination at any location can be obtained (if there is no local attraction) by
establishing a true meridian from astronomical observations, and then reading a
compass while sighting along the true meridian.

Fig. 2.10 Declination east

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