Correct option is A
A prismatic compass is a navigation and surveying instrument which is extensively used to find out the bearing of the traversing. It is the most convenient and portable form of magnetic compass that can either be used as a hand instrument or fitted on a tripod.
The graduated circle of a prismatic compass and surveyor compass is shown in the figure below:
From observation:
The zero of a graduated circle is marked at the south end for the prismatic compass.
Some other differences between the two compass are as follows:
| Item |
Prismatic Compass |
Surveyor’s Compass |
| Needle |
Broad type and does not act as an index |
Edge bar type and acts as index |
| Scale |
Free to float along with broad type magnetic needle |
Attached to the box |
| Bearing |
Whole circle bearing |
Quadrantal bearing |
| Graduations |
Inverted (as graduation have to be observed through a prism) and starts from South, in clockwise direction |
Direct |
| Sighting & Reading |
Can be done simultaneously |
Sighting is to be done first and then the surveyor has to read the northern end of the needle |
| Tripod |
Not essential |
Essential |
