Leading Cadet Training Basic Navigation Leading Cadet Training The Compass and Bearings Lecture 2

The Compass Parts of a Compass Direction of Travel Arrow Rommers 1:25000 1:50000 1:63360 Metric Ruler (cms) Illuminating Mark Under index. Aside north arrow On mag needle Check Point Marker Parts of a Compass Compass Housing Magnifying Glass Magnetic Needle Index Meridian Lines x 4 Orienting Lines North Arrow Orienting arrow Outer Circle = mils Inner Circle = degrees Imperial Ruler (inches) Non-slip Feet x3 Base Plate Lanyard

The Compass The Compass Housing contains a magnetic bar, called the Needle and defines the points of the compass on a rotating bezel. Compass Housing The Magnetic Needle is suspended in liquid, enabling it to move freely, and settle quickly when pointing North. Magnetic Needle The Base Plate is the mounting for the housing and displays a variety of information e.g. Scale ruler. Base Plate

Direction of Travel Arrow The Compass The Direction of Travel Arrow indicates the direction along which you wish to travel or take a bearing. It is fixed in the base plate and the sides of the base plate run parallel to the arrow. Direction of Travel Arrow Index Line The Index Line is a fixed line within the Compass Housing and is in line with the direction of travel arrow. The Index Line marks the bearing you set by rotating the bezel.

The Compass The Orienting, or Meridian Lines are displayed within the rotating Compass Housing and are designed to be aligned parallel with the Eastings on a map. The lines on some compass models are show as one half in red to depict north. Meridian Lines x 4 Orienting Lines

The Compass Nearly all compasses have a scale along the edge of the base plate to enable you to measure distances. Used in conjunction with the scale at the bottom of the map, the compass scale enables you to calculate the distance on the ground. Metric Ruler (cms) Imperial Ruler (inches)

N ? ? ? W E S The Compass NW NE SW SE NNW NNE WNW ENE WSW ESE SSW SSE Points of a Compass N NNW NNE ? NW NE WNW ENE W E ? WSW ESE SW SE ? SSW SSE S

N W E S The Compass NE SW NW SE ESE WNW SSE SSW WSW NNW NNE ENE Points of a Compass ESE NE N S E W SW NW SE WNW SSE SSW WSW NNW NNE ENE 0º & 360º North West : 315º 45º North East 270º 90º South West : 225º 135º South East 180º

Setting a Map with a Compass The Compass Setting a Map with a Compass You can orientate yourself, and the map to the ground by using this system: Lay the compass on the map. Line up the edge of the compass and the compass orienting lines with the Eastings. Turn your body until the red end of the needle is in line with the ‘N’ on the Housing. You and your map are now facing North.

Compass Bearings Points to Note Stand clear of metal objects, they cause the needle to deviate and create inaccurate bearings. Hold the compass as flat as possible to allow the needle to move freely. Look after your compass – try to avoid dropping or knocking it. Store away from other compasses and electrical equipment. Your compass may need replacing if an air bubble forms in the Compass Housing.

Compass Bearings When working from a map we deal with Grid Bearings. When following a compass on the ground we work with Magnetic Bearings. There is a simple system which enables us to convert Grid to Mag and Mag to Grid, The system refers to whether we add or subtract the magnetic variation to convert the bearing. Mag to Grid…………..GET RID Grid to Mag……………….ADD

Compass Bearings Map to Ground Take a Bearing You are at Point A and need to walk to Point B Unfortunately, you can’t see Point B Place the Compass on the Map like so: The direction of travel arrow should point in the direction you wish to go. B A

Compass Bearings Map to Ground Take a Bearing Keeping the Base Plate static – Turn the Compass Housing until the Orienting Lines are parallel with the Eastings And the ‘N’ is pointing to North on your map. B A

Compass Bearings Map to Ground Take a Bearing Read the Compass Bearing shown on the housing from the Index Line Don’t forget the difference between Grid North and Magnetic North. Add this to your bearing. (From Grid to Mag = Add) and you have the magnetic bearing of your course. The next step is to orientate yourself B A x

Compass Bearings Map to Ground Take a Bearing Hold your Compass level and steady. Turn until the red end of the Needle is in line with the ‘N’ on the Housing The Direction of Travel Arrow is now pointing along the route you plotted on the map, and you are ready to travel.

Compass Bearings Map to Ground Back Bearings Point the Direction of Travel arrow at the feature, and take a normal bearing. Turn the Compass Housing until the Orienting Lines are REVERSE parallel with the Eastings Read the bearing and subtract the GMA. Remember – Mag to Grid = Get Rid This is the back bearing of your feature. B A x

Check of Understanding What is the purpose of liquid in the capsule of a compass? Allows the needle to be seen more clearly Increases the needles sensitivity Slows the swing of the needle Allows the needle to settle quickly

Check of Understanding When changing magnetic bearing to grid bearings Which of the following is correct? Mag to grid - Multiply Mag to grid - Add Mag to grid – Get Rid Always an addition

Check of Understanding Which of the following would be more likely to cause magnetic deviation if close to a compass? A cattle grid A large tree Aluminium tent poles A river

Check of Understanding How can a grid bearing from a map on which the magnetic variation is westerly be converted to a magnetic bearing? Add the angular difference between magnetic north and grid north Add the angular difference between grid north and true north Subtract the angular difference between magnetic north and grid north Subtract the angular difference between grid north and true north

Check of Understanding To take a bearing on a map, having set the compass so that the Direction of Travel Arrow points at the feature, what do you do next? Turn the capsule to deduct the grid magnetic angle Turn the capsule so the orienting lines are parallel to the north-south grid lines Turn the map and compass until the needle falls into the orienting arrow Turn the capsule until the needle falls into the orienting arrow

Check of Understanding A line on a map is found to be 110 degrees grid. If magnetic north is 6 degrees west of grid north, what is the magnetic bearing of the line? 98 degrees M 104 degrees M 116 degrees M 122 degrees M

Leading Cadet Training Basic Navigation Leading Cadet Training End of Presentation