Since I believe that the best compass to use for treasure hunting is the lensatic compass, I will limit my descriptions and uses of the compass to the lensatic. Remember, however, that compass basics will work on all compasses.
The lensatic compass consists of the following major parts:
When closed, the cover protects the glass window of the body and the floating dial from damage. It contains a sighting wire mounted vertically in a slit, and two luminous dots (one at each end of the wire) that are used at night.
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The Base is the heart of the compass. It contains:
The lens a mounted on a hinged metal plate. This lens is used to look at the floating dial when making precise measurements. A slit in the metal plate just above the lens is used like the rear sight of a rifle. When the lens plate is pushed against the base, it locks the dial to prevent damage when the compass is carried a the pocket or hanging by a cord. To release the dial, the lens plate must be lifted more than 45 degrees from the base.
When opened flat, the base and cover provide a straight edge with a graduated scale for use on maps. The scale is calibrated for 1:50,000 scale maps. This is a standard military topographical map. Civilian maps, such as those from the US Geological Survey, are 7 1/2 minute series (1:24,000 scale) and so WILL NOT give accurate measurements without complicated conversions.
Remember: The magnetic needle mounted onto the floating dial is affected by metal objects. The larger the object, the farther away you must be from it. Also, power lines produce a large magnetic field around them which also affects the compass. Stay very far away from these power lines.