2. The types of compass that are used
(i) prismatic compass
(ii) surveyor compass.
4. Define:-compass graduation disc is fixed to the box and
magnetic needle is free to rotate above it.
(1).is balanced on a hard and pointed steel pivot
(2). The top of the pointed pivot is protected with agate cap
(3).An aluminium graduated disk
(4) is fixed to the top of the needle.
(5) hinged to the box. In the centre the slit is provided with a
horse hair or a fine wire or thread
(6). The metal frame is provided with a hinged mirror
(7), which can be placed upward or downward on
the frame. It can be slided along the frame.
(8) with a sighting eye vane
(9). The prism magnifies the readings on the graduation disk
5. (10). Dark sunglasses
(11) provided near the line of sight can be interposed if
the object to be
sighted is bright (e.g., sun).
(12) which is about 85 mm to 110 mm supports the pivot of
at its centre.
(13) lid which protects the graduation disc at the same
time permit the direct reading from
(14) which activates
(15) lifts the needle off the pivot.
(16). For pressing spring a knob
or brake pin
(17) is provided on the box. When not in use prism can be
folded over the edge of the box.
6. an instrument used in surveying for measuring horizontal
angles — compare CIRCUMFERENTOR 1, SEMICIRCUMFERENTOR
In this type of compass graduation disc is fixed to the box
and magnetic needle is free to rotate above it.
There is no prism provided at viewing end, but has a
narrow slit. After fixing the line of sight, the reading is
directly taken from the top of the glass cover.
8. Meridian is a reference direction with
respect to which the direction of lines are
There are three types of meridian - True
Meridian, Magnetic Meridian & Arbitrary
9. 1 - True Meridian
It is the reference direction of north pole of
earth from a given station point. It is also called
2 - Magnetic Meridian
It is the direction of north pole indicated by
3 - Arbitrary Meridian
This is any assume direction to a well defined
object. It may be useful for small areas.Direction
of magnetic north with respect to true north is
called magnetic direction.
10. Bearing is the angle which a certain line
make with a certain a certain meridian.
Bearing with respect to true meridian is
called true bearings while magnetic bearing
is the angle which a line makes with respect
to magnetic meridian.
There are two ways to represent the
11. 1) Whole Circle Bearing (W.C.B)
It can be taken 0° to 360°. Quadrants are
taken clock-wisely and angles are also
determined in clockwise direction.
2) Reduced Bearing
Reduced bearing or Quadrantal bearing is the
angle which a line makes from North or South
Pole whichever may be near. It is value is
from 0° to 90°.