Prismatic compass is surveyor’s hand compass provided with a triangular glass prism so adjusted that the compass can read while taking a sight.
It was invented by Captain Kater.
PARTS OF PRISMATIC COMPASS
- CYLINDRICAL METAL BOX: The compass is enclosed in a cylindrical metallic box. The diameter of the box usually varies from 8cm – 12cm. A pivot with sharp point is provided at the centre. Box serves as a protective casing and protects against dust, rain, etc.
- MAGNETIC NEEDLE: Needle is made up of broad magnetized iron bar. It is the main part of a prismatic compass. It measures the angle of line from the magnetic meridian as the needle always points towards the north and south poles at the two ends of the needle when freely suspended.
- PIVOT: Pivot is the centrally located part that provides support to the freely suspended magnetic needle.
- RING/GRADUATED CIRCLE: The graduated circle consists of an aluminium ring that measures the bearing. The ring is graduated from 0-3600 clock wise. 00 marked at south, 900 at west, 1800 at north, 2700 at east. Least count of this compass is 30 min. Figures are engraved inverted.