Sighting Bearings with a Compass

Sighting Compass (compass with mirror) - bearing sighting:

To sight an unknown magnetic bearing from the terrain open the compass mirror to 45 degrees. Sight across the sighting notch at the top of the compass to a distant terrain object - rotate the whole compass to align the sighting line in the mirror with middle of the body of the compass (see the alignment marks). Now twist the compass ring to align the red of the compass pointer with the arrow pointer in the rotating base-plate again using the mirror. check everything still aligns - and read off the magnetic bearing indicated by the pointer on the graduated rotating ring.

If you have a magnetic bearing and want to sight it to the terrain - set the angle on the graduated rotating ring to the known bearing and set the compass mirror to 45 degrees. Rotate yourself and compass until the red of the compass pointer aligns with the arrow pointer in the rotating base-plate. Rotate the compass slightly in your hand to align the sighting line in the mirror with middle of the body of the compass (see the alignment marks). Double check the red pointer again... Sight across the notch in the top of the compass to a distant terrain feature you can use as a persistent reference point for your bearing.

Base Plate Compass (no mirror) - bearing sighting:
With a Non-Mirror compass its the same basic process but is a little more difficult to do the sighting accurately. 2 people working as a team can do it best if accuracy is important.

To sight an unknown magnetic bearing from the terrain - sight approximately first along the compass side edge and rotate or adjust the graduated ring approximately as above then have a helper tell you when the red needle aligns with the arrow in the base as you adjust the ring to center the needle...

If you have a magnetic bearing and want to sight it to the terrain - set the angle on the graduated ring as above - rotate yourself and compass until the red of the compass pointer aligns with the arrow pointer in the rotating base-plate. Then without moving the compass sight along its side edge. Again it works best with a helper - one can hold the compass aligned while the other sights along the edge.

ACM 1/2007

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