We generally use one of two types of compass in the Cadet Corps – the lensatic compass or the Silva compass – and sometimes both depending on what we’re doing. There are many styles and types of compass, but they all share one thing: they point you to Magnetic North. In this lesson, we’ll use a Silva Compass, but we’ll cover the use of the lensatic compass later on. The lensatic compass is the compass used by the military in field operations. It is simple to use and more accurate than most other simple compasses. It includes a sight, sighting wire and lens to more easily focus on the target and read the dial, luminous features for use in the dark, a thumb ring to hold it steady, and a straight edge for measuring distance on 1:50,000 maps. It folds up for protection, and the rear sight locks the needle, which extends the compass life. The movable bezel ring can be used to preset an azimuth. The Silva Compass, or models like it, is a simple, inexpensive compass that’s great for map reading and orienteering. Some have an adjustable baseplate that allows you to adjust for declination, so you can ignore converting grid to magnetic azimuths and back. The compass has direction lines that help align the compass on your map, and assist in pointing along your route. It is not as accurate as a lensatic compass, but works well in an orienteering environment where terrain association is your primary method of finding your way. The key thing to know about a compass is that it points toward Magnetic North. On a Silva Compass, it’s the red part of the compass needle that points north. You've got a dial that turns on your compass. We call it the compass housing (it may also be referred to as a bezel ring. On the edge of the compass housing, you will probably have a scale from 0 to 360. Those are the degrees or the azimuth (or you may also call it the bearing in some contexts). And you might have the letters N, S, W and E for North, South, West and East. If you want to go in a direction between two of these, you would combine them. If you would like to go in a direction just between North and West, you simply say: "I would like to go Northwest ". Turn the compass housing so that northwest on the housing comes exactly there where the large direction of travel- arrow meets the housing. Hold the compass in your hand. And you'll have to hold it quite flat, so that the compass needle can turn. Then turn yourself, your hand, the entire compass, just make sure the compass housing doesn't turn, and turn it until the compass needle is aligned with the lines inside the compass housing. Now, time to be careful!. It is extremely important that the red, north part of the compass needle points at north in the compass housing. If south points at north, you would walk off in the exact opposite direction of what you want! And it's a very common mistake among beginners. So always take a second look to make sure you did it right! A second problem might be local magnetic attractions. If you are carrying something of iron or something like that, it might disturb the arrow. Even a staple in your map might be a problem. Make sure there is nothing of the sort around. When you are sure you've got it right, walk off in the direction the direction of travel-arrow is pointing. To avoid getting off the course, make sure to look at the compass every hundred steps or so. Once you have the direction, aim on some point in the distance, and go there without staring down at the compass. If you are out there without a map, and you don't know exactly where you are, but you know from your experience in the area that there is a road, trail, stream, river or something long and big you can't miss if you go in the right direction… Then all you need to do is to turn the compass housing so that the direction you want to go in is where the direction of travel-arrow meets the housing. And follow the steps you were just shown. But why isn't this sufficient? First, it is not very accurate. You are going in the right direction, and you won't go around in circles, but you're very lucky if you hit a small spot this way. And, this requires you to have a mental image of the area you are in and what direction those landmarks might be in. That’s why using the compass with a map is much, much better. How to “shoot an azimuth” in three easy steps: 1. Turn the dial of the compass to the given azimuth 2. Keep the compass flat in front of you with the “Direction of Travel Arrow” pointing straight ahead. 3. Turn your body so the red (north pointing) needle of the compass lines up inside the red housing on the base of the compass. There are three kinds of azimuth: Magnetic Azimuth: direction expressed as the angular difference between Magnetic North and the direction line (i.e. 140°) Grid Azimuth: the angle measured between Grid North and a line plotted between two points on a map. Back Azimuth: the opposite direction of an azimuth. The back azimuth is 180° from an azimuth. For azimuths more than 180°, subtract 180. For azimuths less than 180°, add 180. A back azimuth of 180° is either 0° or 360°. The Protractor. There are several types of protractors – circular, half-circle, square, and rectangular. All have a scale around the outer edge and an index mark in the middle. On military protractors, you read the inner of the two scales because it is broken into degrees from 0 to 360. Each tick mark on the degree scale represents one degree. You have several coordinate scales for measuring grid coordinates, one for each of the most common map scales you might use. Index – where the N/S and E/W lines cross in the middle. It’s the central point from which you measure an azimuth. 360 Degrees - usually the inner of two types of direction marks Mils – the outer measuring marks found on Army protractors. Used in field artillery plotting. You can ignore them (or even carefully cut them off your protractor!) Next, we’ll learn how to use the protractor to determine an azimuth between two points. 1. Find the two points you want to measure an azimuth between (Figure 49). 2. Line up the protractor so the index lines are exactly parallel to the map’s grid lines (Figure 50). 3. Align a straight edge along both points. Check carefully to see where it crosses the protractor’s degree scale. 39°! (Figure 51).