Prismatic Compass:

It is the commonly used compass for engineering surveys and is suitable for surveys where speed is more important than accuracy, for example, the preliminary surveys of road, pipe line or railway line alignments and rough traversing etc. Figure shows the different constituents of a prismatic compass in their final assembled form.

Figure : Prismatic Compass

The aluminium ring of prismatic compass has a magnetic needle marked with N-S along the diameter of the ring. The graduations are itched from 0^o to 360^o in clockwise direction with zero marked at south end of needle and 180^o at the north end (Figure). The itching is marked in inverted fashion so that they are read in correct way when viewed through the reflecting prism. Each degree in graduation is divided into half to give a least count of 30'.