Reading A Lensatic Compass Flashcards
Bezel ring
The bezel holds the upper glass crystal in place. It helps preset a direction for night Compass navigation. It contains 120 clicks when fully rotated; each click equals 3°
Compass dial
Floats free when in use. It is locked in place by closing the eyepiece. It contains two complete circular scales, one in degrees (read scale) and one in Mils (black scale). The magnetic arrow is found on the Compass
Cover
The cover contains a sighting wire. When closed it protects the face of the Crystal. When at a 90° angle to the other half of the Compass, it can be used to sight on objects.
Thumb loop
Retaining device to secure the Compass in a closed position. Used when holding the Compass in position for sighting on objects.
Black index line
Stationary line used as a reference for determining direction. When held properly, it identifies the direction the Compass is pointing.
Sighting wire
Provides an exact azimuth for objects. Can be used for compass calibration. Also used with steering marks.
The declination diagram
Indicates the difference between true North, grid north, and magnetic north. Used when converting a magnetic azimuth shown on your lensatic compass dial to a grid azimuth on your map. You can also use it to convert a grid azimuth a magnetic as well. The declination diagram is different for every map
True North
Indicates the direction of the geographic North Pole. True North is marked by a star (*) on the declination diagram
Grid north
Indicates the direction in which the north-south gridlines of a map are oriented. These may not or may correspond with true or magnetic north, depending on where you are located in the world
Magnetic north
In the case the north direction of your Compass reading. It is usually different than true North because the earths magnetic field causes the Compass arrow to point to a magnetic area around instead of directly at the north pole. Magnetic north direction will change depending on your geographic location and also with time. Magnetic north is marked with a half arrowhead
G-M angle
The difference between grid North and magnetic north shown in degrees You will add or subtract this value from the magnetic or grid azimuth when converting from one direction to another.
Orienting the map
Adjusts the map so that north on the map points to North on the ground and the information on the map will match the features on the ground
Orienting a map
Step one) determine the direction of magnetic north and the G-M angle on the declination diagram
Step two) align the straightedge on the Compass with a north-South grid line
Step three) rotate the map and compass together aligning the magnetic Arrow and the fixed black index line
Step four) rotate the map and compass together until the Compass arrow is aligned with the magnetic arrow
Step five) check the Compass reading
Holding a Compass
The two most common are the center hold technique and the compass to cheek technique
Center hold technique
Fast and easy. Used under any visibility conditions without taking off your helmet or removing your rifle from sling arms.
Center hold technique
Open the Compass, set the lens (rear site), position your thumb, position your fingers, position your elbows.
Compass to cheek technique
More accurate and ideal when employing intersection and resection techniques and are more accurate azimuth required.
Compass to cheek technique
Position the cover, fold the rear site, align the front site hairline, read the azimuth
Determining an azimuth
Raise the Compass to Eye level, aligned the center of the siding slot, read the azimuth
Determining the azimuth
The azimuth, in degrees, is the red number on the dial lying directly under the black line of the Compass Crystal. The azimuth, in Mils, is the black number on the outer perimeter of the doubt
Selection and use of steering marks
It will defined guiding object on the azimuth. Can be natural or man-made but fixed and stable. While navigating, day or night, every step you take should be toward a selected steering Mark.
Setting a course
Set the azimuth directly under the black index line (Holding the Compass in this position, rotate the bezel ring until the luminous indicator is over the North arrow of the dial. The direction indicated by the open Compass is the desired course)
Rotate the bezel to North arrow (Holding them and set a compass in this position, rotate the bezel ringing until the luminous indicator is over at the North arrow of the doubt. The direction indicated by the open Compass is the desire course)
Proceeding along an azimuth
Align the magnetic compass arrow with the luminous line, proceed forward towards the desired as well, select a steering Mark
Looking positions by means of intersecting azimuths
Used to locate distant or inaccessible points or objects such as enemy danger areas. There are two methods of intersection: the map and compass method and the straight edge method.
Map and compass method
Orient map, Mark your position on the map, determine the magnetic azimuth, convert the magnetic azimuth, draw a line on the map, move to a second known point, determine the grid coordinates
Straight edge method
Compass not available.
Orient the map, locate your position, rotate using a straight edge, draw a line, repeat to next position, determine coordinates
Dead reckoning
Follow the desired as much on your Compass, while keeping a pace count until you have traveled the distance to your destination
Pace count
A pace Count is equal to two natural steps, about 60 inches long or 1.5 m. To accurately use pace count method, you must know how many paces it takes to walk 100 m. A pace is counted whenever your left foot touches the ground
Shifting techniques
Combination of Compass azimuth and knowledge of intended route.
Checkpoints
Checkpoints are typically terrain or man-made features design as such in planning. Line checkpoint is far superior to a point checkpoint for navigation at night.
Interference and accuracy
Vulnerable to iron and powerlines that emit electromagnetic fields
Limitations
55 m high extension powerlines 10 m field gun, truck or tank 10 m telegraph/telephone wires or Barbwire 2 m machine gun .5 m steel helmet or rifle
Inspections
Inspect whenever you use Compass. Inspect floating dial to ensure that the glass and crystal parts are not broken, the numbers on the dial are legible, the floating doubt does not stick, the sighting wire is straight, the bezel ring produces distinct clicks turn
Care and maintenance
Rinse with freshwater, especially after exposure to salt water
Brush off dirt and grime
Ensure the ridges on the bezel ring are free of dirt
Check movement of the rear sight to ensure it is free moving
