The Lensatic Compass
GPS devices and compasses are key tools in land navigation. When it comes to military courses and learning the basics of land navigation, the lensatic compass is used. This compass is the most common and simplest instrument for measuring direction. Directions read by any instrument is commonly referred to as an azimuth. An azimuth on a lenstatic compass can be found in two scales: mils (0-6400 scale) or degrees (0-360 scale). In land nav, we advise you focus on using degrees.
Check your compass to ensure the compass you have been issued is in working order. The compass is a delicate instrument that should be cared for an checked on before use. It is very important to open the compass and ensure the floating dial which contains the magnetic needle (where azimuth measurements are read) has readable numbers and is in working order. The glass and crystal parts of the compass should also be intact. The user should also ensure the floating dial moves accurately and does not stick in place. This can be done by rotating while holding the compass level to ensure the floating dial rotates with movement. The sighting wire, the equivalent of a front sight post, should be checked to ensure the wire is straight and can be accurately used to assess walking direction when an azimuth is being measured. If traveling with the compass unfolded, ensure the rear sight is completely folded down onto the bezel ring. This locks the floating dial, prevents vibration, and protects the crystal and rear sight from damage.
Note: Metal objects and electrical sources can affect the performance of a compass. Separate from power lines field guns, trucks, tanks, telephone wires, and barbed wire to ensure proper functioning of the compass. Nonmagnetic metals and alloys do not affect compass readings.
How to Use the Compass
There are two main techniques to using a compass: centerhold and compass-to-cheek
Centerhold Technique- Open the compass fully so that the cover forms a straightedge with the base. Move the lens (rear sight) to the rearmost position, allowing the dial to float freely. Next, place your thumb through the thumb loop, form a steady base with your third and fourth fingers, and extend your index finger along the side of the compass. Place the thumb of the other hand between the lens (rear sight) and the bezel ring; extend the index finger along the remaining side of the compass, and the remaining fingers around the fingers of the other hand. Pull your elbows firmly into your sides; this places the compass between your chin and your belt. To measure an azimuth, simply turn your entire body toward the object, pointing the compass cover directly at the object. Once you are pointing at the object, look down and read the azimuth from beneath the fixed black index line. (See Figure 8-2.) This preferred method offers the following advantages over the sighting technique:
It is faster and easier to use.
It can be used under all conditions of visibility.
It can be used when navigating over all types of terrain.
It can be used without putting down the rifle. However, the rifle is slung well back over either shoulder.
It can be used without removing eyeglasses.
Compass-to-Cheek Technique- Fold the cover of the compass containing the sighting wire to a vertical position; then fold the rear sight slightly forward. Look through the rear-sight slot and align the front-sight hairline with the desired object in the distance. Glance down at the dial through the eye lens to read the azimuth. (See Figure 8-3.)
The compass-to-cheek technique is used almost exclusively for sighting. It is the best technique for this purpose.
Following an Azimuth
Centerhold Technique- To follow an azimuth, assume the centerhold technique and find your desired azimuth. Proceed forward in the direction of the front cover’s sighting wire, which is aligned with the fixed black index line that contains the desired azimuth.
Compass-to-Cheek Technique- Note, this is an added note and not a textbook method. Use at your own discretion. You can use the compass-to-cheek technique to sight in an azimuth. When looking at the desired azimuth, pick an identifiable object that is in line with your sighting wire. Walk towards that object.
A pace count is the soldier's main tool to keep track of the distance that is being traveled. A pace count is established by measuring how many paces it takes to travel 100 m. Stepping off with the right foot, a pace is counted every time the soldier's left foot strikes the ground. Two pace counts should be done: walking and running.
Walking Pace Counts- these are used when keeping track of distance and following an accurate azimuth is more critical, like traveling through thick woods.
Running Pace Counts- Running pace counts can be done to speed up the travel time and are typically done when traveling safer routes like roads and trails that lead to easily identifiable intersections or terrain features. Running pace counts may be used through the woods when following an azimuth but can be a little more risky in terms of accuracy.
Note: ensure you walk or run with the same pattern and rhythm you would use in the field. The accuracy of your pace count to how you travel naturally is crucial in making accurate measurements in the field.
Methods to Keep Track of Distance
It can be easy to loose track of the distance being traveled if distractions occur. Therefore, many use methods to keep track of the distance being traveled. Some methods include:
Putting a pebble in a pocket every 100 m traveled
Writing tick marks in a notebook
Using a Ranger pace count bracelet. This bracelet has beads that can be moved over for every 100 m traveled.
We advise you use a method to keep track of distance. Either one of the above methods, or design another, we do not recommend relying on mental tracking and memory alone.
Conditions That Affect Pace Count
Certain conditions affect the pace counts in the field. Here are some considerations for shifts in a standard pace count:
Walking Up a Slope- Walking up a slope would shorten the pace count; therefore, it will take more paces to travel 100 m up a slope.
Walking Down a Slope- Walking down a slope would lengthen the pace count; therefore, it would take less paces to travel 100 m down a slope.
Head Winds- A strong wind towards you tend to shorten pace counts and require more paces to travel distances.
Tail Winds- A strong tail wind behind you tend to lengthen pace counts and require less paces to travel distances.
Surfaces- Surfaces like sand, gravel, mud, snow, and others tend to shorten the pace count and require more paces to travel distances.
Elements- Falling snow, rain, or ice tend to shorten pace counts and require more paces to travel distances.
Clothing- Excess clothing and boots with poor traction tend to shorten pace counts and require more paces to travel distances.
Visibility- Poor visibility such as in fog, rain, or darkness, tend to shorten pace counts and require more paces to travel distances.
Headquarters, Department of the Army. (2013). Map Reading and Land Navigation (FM 3-25.26).