Compass

Page 3

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:

The Cover

The Base

The Lens

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.

The Base is the heart of the compass. It contains:

• A floating dial, mounted inside the body. The dial can move freely when the compass is held level. The dial has a three luminous markings on it. A luminous arrow, and two letters "W" (west), and "E" (east). The dial has two sets of numbers etched into the outer rim. The outer most of the two is mils (mils is a system used by the military and not very useful for our purposes). The inner most of the two is degrees (more on this later). The degree scale may be black or red. When allowed to swing free, the dial will always point north. 

• The glass window of the base, through which you observe the floating dial, is fixed and has a black line (index line) that is lined up with the sighting wire in the cover.

• A bezel ring is attached to the rim of the base. It is knurled and, when turned, "clicks." If the bezel is turned one complete turn, there will be 120 clicks. One click will equal 3 degrees (more on this later). An outer glass window is attached to the bezel. This windows has a "short luminous line".  This line rotates as the bezel is turned and is used at night (more on this later).

• A thumb loop is attached to the base. This loop is used when actually using the compass for sighting.

• 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. 

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