Surveyor compass versus Prismatic Compass -  Compass used in Surveying

COMPASS USED IN SURVEYING

Parameter	Surveyor’s  Compass	Prismatic Compass
Magnetic Needle	Edge bar needle is  used and it act as index	Broad needle is used  and it is hidden below the aluminium ring  and does not act as index.
Graduation	Graduated ring is attached  to the box and ring rotates with box. Graduations vary from 00 to 900  in the four quadrants.  Zero points are marked with N and S.	Graduated ring attached to the needle and remains stationary. Graduations vary from  00 to 3600 clockwise  with zero at south end.
Sighting Vanes	Readings are taken by directly looking  through the glass  and reading the north end of needle.	Readings are taken  through the vertical  side of the prism provided  at the eye vane.
Reading	Sighting and reading are done separately  and that too from different positions. After sighting the object,  the observer move around and takes the reading at North end of needle.	Sighting and reading  are done simultaneously.
Support-Requirement	Tripod is compulsory.	Tripod may or may not be used.

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