As there are three different kinds of North points, they are three types of bearings according to the North point from which they have been measured.
- Magnetice Bearing: is one taken with a compass.
- Grid Bearing: Is one measured on the map with the compass used as a protractor.
- True Bearing: Cannot be measured direct, but must be calculated from one of the other two.
Remember this Simple Rule.
- Grid to Mag-----ADD
- Mag to Grid ----GET RID
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You are wanting to go from the car park to the site of an old fort and the direction is, as shown on the map .
Lay the edge of the compass so it bisects the car park and the site of the fort. making sure that the direction of travel arrow is pointing in the direction you wish to go. Note the position of the magnetic needle and the orienteering lines at this stage.
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Holding the compass steady turn the compass bezel until the orienteering lines are running vertical and alongside the vertical lines on the map (Eastings).
Then read off the bearing at the index line on the compass and this is your grid bearing. Remember you will ahve to convert this to a magnetic bearing.
Points to Remember.
Keep the compass at least these distances away to avoid incorrect readings.
- Buildings and high tension cables and sub stations - 55 to 60 metres.
- Vehicles, pylons, metal gates and cattle grids- 18 -20 metres.
- Binoculars, electronic equipment and radios - 0.5 metres.
These distances are only a guide, just be aware of your surroundings when using a compass.
Note: Also be aware of any metal you may have on your person when using a compass especially when you are taking a magnetic bearing where you tend to hold the compass close to your body. thigs like buckles, watches and one for the ladies, wire in their bras, this does affect the magnetic needle. Also hand held GPS and mobile phones.