how to use compass
Post on 07-Mar-2016
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DESCRIPTIONmanual how to use the Compass
1/9 Scout Skills Compass The Scout Association 2000 Item code: FS315074(Format Revision Aug 2000)The Scout Association, Information Centre, Gilwell Park, Bury Road, Chingford, London E4 7QW. Email: firstname.lastname@example.orgWebsite www.scoutbase.org.uk Direct: 020 8498 5400 Local rate call: 0845 300 1818 Fax: 020 8498 5407
0845 300 1818
Scout SkillsCompassINFORMATION SHEET
A compass is an instrument with a magnetisedneedle which points to (magnetic) north and istherefore used for determining direction. Theycome in different shapes and sizes and indeed,the use of suspended magnetic ore (whichalways comes to rest in a north-south direction)was used many centuries ago as a primitive formof compass. Today, in one form or another,compasses are used on land, at sea or in the air,to help people to specify direction.
Types of compass
Air damped compass - This is the simplest andcheapest form of compass and does little morethan indicate the approximate direction ofmagnetic north. It takes a long time to stabiliseand the slightest movement makes the needlemove. This compass should never be used forany sort of hike or expedition.
Simple map setting compass - It is a liquid filledcompass with only magnetic north marked on itand can be clipped onto the side of a map. It isuseful for positioning a map until whatever is infront of you in reality, is in front of you on themap. This can only be approximate as there isno allowance for magnetic variation, that is, thedifference between magnetic north and grid(map) north. (This is explained in more detaillater on).
Prismatic compass - This is a more expensivetype of compass with a prism which enables acompass bearing to be taken while sighting yourobjective. It can be more accurate than othercompasses but it is harder to use and thereforeshould only be used once the basic principles ofmap and compass work have been mastered.
Silva type compass - This consists of amagnetised needle suspended in an alcohol filledhousing. The liquid helps to 'dampen' movementof the needle enabling it to be read more quicklythan air damped compasses. The compass
housing has etched orienting lines and anorienting arrow, whilst the baseplate (on whichthe housing is mounted) has the direction oftravel arrow and map scales etched onto it. Thiscompass allows for bearings, an accuratemethod of determining direction, to be workedout and is therefore the compass of choice forhiking and expedition type activities.
Why use a compass?
As you can see, it is possible to have a varyingquality of compass depending upon what job ithas to do and of course, ultimately, how muchyou pay for it!
Apart from determining the direction of north, acompass enables you to work out a compassbearing. This is the angle measured in thenumber of degrees between 0 and 360 whichtells you the direction from one place to another.We call the direction north '0' and therefore, itfollows that east is 90 degrees, south-west is 225degrees and so on.
If we just used the points of the compass, (north,south, east, west and so on) we would only get
2/9 Scout Skills Compass The Scout Association 2000 Item code: FS315074 (Format Revision Aug 2000)The Scout Association, Information Centre, Gilwell Park, Bury Road, Chingford, London E4 7QW. Email: email@example.comWebsite www.scoutbase.org.uk Direct: 020 8498 5400 Local rate call: 0845 300 1818 Fax: 020 8498 5407
eight different directions (or possibly 16 or 32 atmost if we further divided the compass points,for example, south-southwest or north bynortheast and so on). By using bearings, we canhave 360, which enables us to be much moreaccurate.
Once we have determined a direction (andbearing) in which to travel, it can then bechecked at regular intervals to confirm that weare still going in the correct direction whether ornot our destination can be seen.
When using a compass proficiently, it isnecessary to be able to: Take a bearing - determine the angle
between north and the direction of an objectin terms of degrees;
Walk on a bearing - use a bearing to get to adestination without necessarily using a map;
Set a map - use a compass to correctlyposition a map in order to represent what canactually be seen.
(Details on how to do these are covered in theTeach Yourself section.)
The three norths
When working with a map and compass, thereare three different 'norths' to be considered!Fortunately, in the United Kingdom, for practicalpurposes, we only have to consider and workwith two of them.True north - Each day the Earth rotates about itsaxis once. The ends of the axis are the trueNorth and true South poles.Grid north - The grid lines, pointing to grid north,on Ordnance Survey maps divide Great Britaininto 100 kilometre sections. They are thenfurther sub-divided into one kilometre squares,east of an imaginary zero point in the Atlantic
Ocean, west of Cornwall. The majority of gridlines are 1.5 degrees west of true north and aretherefore useful lines to refer to when takingbearings.Magnetic north - A compass needle points to themagnetic north pole. Unfortunately, it is not inthe same position as the true North pole. Themagnetic north pole is currently located in theBaffin Island region of Canada, and from theUnited Kingdom, it is west of true north. Thedifference between grid north and magnetic northis known as the magnetic variation and its valuecan be found in the orientation panel or marginof an Ordnance Survey map.
As true north is only about 1.5 degrees off gridnorth, it is so small that it is normally disregardedand only grid north and magnetic north are used.
The magnetic variation, (the difference betweenmagnetic north and true north), is caused by theNorth and South poles not being directly'opposite' one another. The lines of the Earth'smagnetic field do not run in a regular pattern asthey are affected by other local magnetic forcesand the magnetic pole is always on the move.Some of these lines of magnetic variation areeast of true north and others west of true north.Between the east and west lines there is a line ofzero magnetic variation where the compass doespoint to true north - this line is known as theagonic line currently running through easternCanada, United States of America and SouthAmerica.
However, not only does the magnetic variationchange as you move across the Earth's surface,it also changes with time. In the UnitedKingdom, the magnetic variation in 1991 wasabout 6 degrees and decreasing at anapproximate rate of 0.5 degrees every threeyears.
It is important to check the magnetic variationregularly, and this can be found on a map'sorientation panel or margin. Remember also tocheck the year the map was printed, as a mapthat is 20 years or so old, could be up to 3 or 4degrees out! In fact, the magnetic variation alsovaries from side to side and top to bottom oneach and every map but these details can alsobe found on the map.
3/9 Scout Skills Compass The Scout Association 2000 Item code: FS315074 (Format Revision Aug 2000)The Scout Association, Information Centre, Gilwell Park, Bury Road, Chingford, London E4 7QW. Email: firstname.lastname@example.orgWebsite www.scoutbase.org.uk Direct: 020 8498 5400 Local rate call: 0845 300 1818 Fax: 020 8498 5407
This magnetic variation is important whencombining a map and compass as you need toconvert bearings from 'map to field'. To convertgrid bearings (which are indicated by a map) tomagnetic bearings (as per the compass pointingto magnetic north), add the current variation byturning the compass housing anti-clockwise. Forexample, if the current variation was 6 degrees,a grid bearing of 122 degrees would become 128degrees. This is what the dial should be set at.The reverse is true for converting a magneticbearing to a grid bearing; that is, subtract thecurrent variation.
For expeditions abroad however, some parts ofthe world will not only have a different value, butmay also be east of true north, in which case,when converting from grid to magnetic bearings,the magnetic variation should be subtracted fromthe compass bearing.
Further information and resources
Ask other Leaders experienced in the use of themap and compass for advice and ideas. Do theyknow of opportunities for practising or learninghow to use them?
There are also plenty of books available on thissubject, both at a beginner's level, and moreadvanced.
Camping and Outdoor centres and other highstreet shops selling camping and hikingequipment may be able to offer advice.
4/9 Scout Skills Compass The Scout Association 2000 Item code: FS315074 (Format Revision Aug 2000)The Scout Association, Information Centre, Gilwell Park, Bury Road, Chingford, London E4 7QW. Email: email@example.comWebsite www.scoutbase.org.uk Direct: 020 8498 5400 Local rate call: 0845 300 1818 Fax: 020 8498 5407
Understanding how to use a compass is likemany other activities; it's easy when you knowhow! Practice is also the only way to get it rightand remember it. Although this sheet can helpyou through the different stages, the onlyeffective way to learn is to go out and use thecompass for real. Ask experienced Leaders foradvice and also take part in a hike or expeditionto put the skills into practice.
Up to one hour may be required to becomefamiliar with the parts of a compass and theprinciples of how to use it, especially inconjunction with a map, but more time will berequired in shorter sessions to put it into practice.
A Silva (type) compass and an Ordnance Surveymap of the area you are in.
Learning all about it
Before having a go, you will need to read theInformation Sheet if you have n