Part 1 - How to use a compass
Step 1 - Always ensure that the map is facing the correct way. On Irish OS maps north is always to the top of the map as you are reading it
Step 2 - Say for example I want to navigate from the summit of Kanturk or Brown Mountain to the summit of Scarr as per the exert above. Place the baseplate of the compass on the map between the two points ensuring the straight edge of the compass intersects both points (You can also use the black lines from the baseplate (see compass image above) as your straight edge - hold the compass with the straight edge on the map for the next stage
Step 3 - NB that the Direction of travel arrow (as per the image above) points in the direction you wish to travel
Step 4 - Next step involves twisting the Compass dial so that the Orienting arrow / Orienting Lines match the Easting (blue) lines on the OS map - this has to be precise
Step 5 - Check that the straight edge still intersects the two points on the map (sometimes while twisting the compass dial you can inadvertently move the compass)
Step 6 - Once you are certain that you have done all the above steps correctly you can now remove the compass from the map
Step 7 - Holding the Compass horizontally in front of you, position the compass approx at the base of your sternum and turn yourself around until you get red on red. You will notice from the compass image that there is the RED orienteering arrow and the RED Magnetic Needle. When they are positioned together the direction of travel arrow will point you in the direction you need to travel
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DECLINATION - I will not go into the finer details of the declination principle, however if you would like to know more about it please follow this link
Declination basically refers to the difference between True North (also known as Geographic North), Grid North and Magnetic North .
True North: Geographical North pole.
Grid North: This is shown on the North - South grid lines on the map and may be up to 2 degrees different to true north.
Magnetic North: The earth's magnetic pole doesn't correspond to the Geographic North Pole and because the earth's core is molten, the magnetic field is always shifting slightly (variable point somewhere north of Hudson bay in Canada) The red end of your compass needle is magnetized and wherever you are, the earth's magnetic field causes the needle to rotate until it lies in the same direction as the earth's magnetic field.
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With all this in mind it is necessary to adjust your compass to account for Declination. All OS maps have an information section on the right hand side called The National Grid. Located here is the Declination correction required for that area. For example OS Map Discovery Series 56, 4th Edition has a declination correction of 6 degrees 26 minutes West of Grid North (you do not have to account for minutes on the compass) - so adjust your compass 6 degrees to the West dec marked on your compass (turn compass wheel anti clockwise)
NB. Depending on where you are in the world the direction of declination will vary. It is important to consult your local map always.
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