Lecture

Leading Cadet Training

Basic Navigation

2The Compassand Bearings

The Compass

LanyardBase Plate

Non-slip Feet x3

Imperial Ruler(inches)

Metric Ruler(cms)

Magnifying Glass

Check Point Marker

Direction of TravelArrow

Rommers1:250001:500001:63360

Compass Housing

Index

Meridian Lines x 4Orienting Lines

Outer Circle = milsInner Circle =

degrees

Illuminating MarkUnder index.

Aside north arrowOn mag needle

North ArrowOrienting arrow

Magnetic Needle

Parts of a Compass

The Compass

Base Plate

Compass Housing

The Base Plate is the mountingfor the housing and displays a variety of information e.g. Scale ruler.

The Compass Housing containsa magnetic bar, called the Needleand defines the points of the compass on a rotating bezel.

Magnetic Needle

The Magnetic Needle is suspendedin liquid, enabling it to move freely, and settle quickly when pointing North.

The Compass

The Index Line is a fixed line within the Compass Housing and is in linewith the direction of travel arrow.

The Index Line marks the bearingyou set by rotating the bezel.

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 thesides of the base plate runparallel to the arrow.

Index Line

Direction of Travel Arrow

The Compass

The Orienting, or Meridian Lines are displayed within the rotating Compass Housing and are designedto 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 4Orienting 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.

Imperial Ruler(inches)

Metric Ruler(cms)

The CompassPoints of a Compass

N

S

EW

?NE

SW

NW

SE

?ESE

?

WNW

SSESSW

WSW

NNW NNE

ENE

The Compass

ESE

NEN

S

EW

SW

NW

SE

WNW

SSESSW

WSW

NNW NNE

ENE

0º & 360º

270º

180º

90º

Points of a Compass

45º North East

South West : 225º 135º South East

North West : 315º

The CompassSetting a Map with a Compass

You can orientate yourself, and the mapto 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 BearingsPoints 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 BearingsWhen 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

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.

Compass Bearings

BB

AA

Take a Bearing

Map to Ground

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.

Compass Bearings

BB

AA

Take a Bearing

Map to Ground

Read the Compass Bearing shown on the housingfrom 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

Compass Bearings

BB

AA

Take a Bearing

Map to Ground

x

Compass Bearings Take a Bearing

Map to GroundHold 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.

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.

Compass Bearings

BB

AA

Back Bearings

Map to Ground

x

Check of UnderstandingWhat is the purpose of liquid in the capsule of a compass?

Allows the needle to settle quickly

Allows the needle to be seen more clearly

Slows the swing of the needle

Increases the needles sensitivity

Check of UnderstandingWhen changing magnetic bearing to grid bearings

Which of the following is correct?

Always an addition

Mag to grid - Multiply

Mag to grid – Get Rid

Mag to grid - Add

Check of UnderstandingWhich of the following would be more likely to cause

magnetic deviation if close to a compass?

A river

A cattle grid

Aluminium tent poles

A large tree

Check of UnderstandingHow can a grid bearing from a map

on which the magnetic variation is westerly be converted to a magnetic bearing?

Subtract the angular difference between grid north and true north

Add the angular difference between magnetic north and grid north

Subtract the angular difference between magnetic north and grid north

Add the angular difference between grid north and true north

Check of UnderstandingTo 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 until the needle falls into the orienting arrow

Turn the capsule to deductthe grid magnetic angle

Turn the map and compass until the needle falls into the orienting arrow

Turn the capsule so the orienting lines are parallel to the north-south grid lines

Check of UnderstandingA 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?

122 degrees M

98 degrees M

116 degrees M

104 degrees M

Leading Cadet Training

Basic Navigation

End of Presentation