Task 1: Setting a Course
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Now, we can start actually using our compass. The whole premise of the lensatic compass is to be able to look at a distant object or topographic feature through the sights of our compass and then measure the azimuth of that feature from our location. This is called 'sighting on' or 'sighting off of' the feature.
In our first example, we go through the process of sighting off a feature and simply heading directly for it. This is the simplest operation of a lensatic compass and is unaffected by issues such as declination. A map, while helpful, is not absolutely necessary. In this example, we suppose that you are on a hilltop in the woods and wish to get to a (different) visible hilltop nearby. However, as soon as you leave your hilltop, you will no longer be able to see your destination due to all the foliage. So, you must first set a course with your compass.
First, open your compass so that the cover is at a right angle to the rest of the compass body. Flip up the lens bracket just until the dial floats freely and without restriction from the lock. The lens should be at about a 30-45 degree angle. Fold the thumb loop all the way down until it stops against the body of the compass. Insert your straight thumb trough the loop, with the compass resting on top of it. Curl your index finger in front of your thumb under the compass for further support. Curl the rest of your fingers into a fist with your middle finger holding the outside of the thumb loop just below your thumb. This is the grip used for sighting.
While looking at your destination hill, bring the compass up to eye level. The spot on the back of your hand behind your thumb (circled in red above) should rest against your face (probably against your cheek but that may vary a bit by person). Now, with the compass held level, look through the sight slot at your destination hilltop and align the sight wire directly on the peak. Your view should look about like the left side image below. Without moving the compass, glance down through the lens to read the azimuth. The black index line will be directly over the correct azimuth, as in the right side image.
The azimuth in the above image is reading 120 degrees. Bring the compass down from your eye (you can break your sighting grip now). Holding the compass level, look at the dial from directly above. Re-align the index line to 120 degrees (below, left). Then, rotate the bezel until the bezel indicator is directly aligned with the North arrow (below, center).
At this point, anytime you want to check your course, you need only to fully open the compass and line up the north arrow with the bezel indicator. The direction that the body of the compass is pointing (along the sight wire) is the direction to your destination, and should be the way your headed. This compass has tritium illumination, allowing the checking of ones course in dim, or even dark, conditions (above, right image). The luminous indicators in the cover show the direction that the compass is pointed. If you magnify the image, you can see the azimuth is easily read.
Before starting for your destination, look along your azimuth through the compass sights again and pick a small, nearby landmark that will remain visible along your entire path until you reach it. This may be a unique tree, small rock outcropping, or any object that can be positively identified from the surroundings. You should try to follow a string of such smaller landmarks on the way your destination. Each time you reach a landmark, find a new one along your bearing using the compass sights and head towards it. Ideally, these reference landmarks should be 400-500 yards away, but circumstances may require otherwise.
If a map is available, take note of any major terrain or man-made features that you will cross on your path (lakes, streams, roads, etc). These will help orient you as you cross them. Conversely, not seeing them can alert you that you might be off course! It is useful to count your paces as you are heading to a destination, as an excessive pace count can also alert you to check your bearing. See our Basic Navigational Skills article for more info. You are now ready to start for your destination.
In many cases, there may not be a reference landmark directly along your desired bearing. In that case, you may need to use a landmark slightly off your desired bearing and correct your course using the following procedure.
Let's say you've reached your first reference landmark from your starting point. You are unable to see Landmark 3, from your current position. No usable landmark is available directly on your desired bearing of 120 degrees but Landmark 2 is close, at a bearing of 130 degrees. You will then head to an imaginary point, between Landmark 2 and your desired course. In this example once you reach this point, Landmark 2 will be directly to your right.
You've reached the midpoint. You will now use a back azimuth to put yourself back on course. A back azimuth is simply the opposite direction of any given point on the compass. For example South at 180 degrees is the back azimuth of North at zero degrees. To find the back azimuth of your desired bearing, simply add or subtract 180 degrees. It is generally easier to add for bearings from 0-180 degrees and subtract for bearings 180-360 degrees. This helps avoid possible math errors caused by crossing zero, but the result is the same either way. Here, we want the back azimuth of 120 degrees (our desired bearing) so we add 180 to 120 to get a back azimuth of 300 degrees.
Now, locate and take a sighting off Landmark 1 again. Since you're at a point between the 120 degree desired course (back azumith 300 degrees) and the 130 course to landmark 2 (back azimuth 310 degrees), if you are at the exact midpoint between Landmark 2 and the desired course, the azimuth reading you get will be about 305 degrees. You don't actually need to be at the exact midpoint, anywhere between Landmark 2 and your desired path will do.
You want this back azimuth to read 300 degrees. So, head towards your desired course and away from Landmark 2 (towards the top of the image), occasionally checking the azimuth to Landmark 1, until the azimuth reads 300 degrees. If the azimuth falls below 300 degrees, you've gone too far and simply need to go backwards until it reads 300 degrees. Once the azimuth to Landmark 1 reads 300 degrees, you are standing back on your original bearing and can now sight a new landmark (Landmark 3 in this example) and continue on your way.​​​