Transcript The compass : Introduction [Power Point

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Silva Compass – Parts
How a Compass Works
Setting the Map with a Compass
1) Twist the bezel so that the “Shed” is at the top.
2) Lay the compass along one of the
North/South gridlines pointing towards the
top of the map
3) Rotate the map with the compass held still and put the RED IN THE SHED.
I.e. the red arrow in the red shed, the map is now set to North!
Exercise:
Using your map and compass, set the map to North
Taking a magnetic (Compass) Bearing
1) Point the compass direction of travel arrow
at the object that you wish to take the bearing of
2) Rotate the bezel until the red is in the shed
3) Read off the number at the direction of travel arrow – this is the magnetic
bearing
Exercise
Using your compass,
Take 3 different bearings from the room your are in,
For example a bearing to the fire extinguishers,
Bearing to the door
Or a bearing to light switches
How to take a Grid / map bearing
Lie the edge of the compass along the place you are at and the place you are
going to, i.e. from the track
to the church with the direction of travel arrow pointing in the intended direction
2) Turn the bezel until the lines inside the bezel line up parallel with the grid lines on the map
3) Read off the number, this is your grid bearing.
Note that we ignore the North arrow when doing this, as our bearing is a grid bearing from grid north
Magnetic variation:
The magnetic variation of the earth changes currently it is set at 4
degrees. This means that a bearing taken from a map will be 4 degrees
out. Likewise a “real life” bearing, when transferred back to the map
will also be 4 degrees out in the other direction. There is another rule:
Mag to grid – get rid
Grid to mag – add.
So if we have taken a grid bearing from a map we have add 4 degrees
And if we are taking a bearing and transferring to the map we subtract 4
degrees.
Exercise:
You are at the summit of Conic Hill the grid reference is 433 924,
You have just come around after being knocked out by a pigeon dropping
its lunch
it is extremely foggy and you cant see your hand in front of your face.
All you have is your map and compass and you need to get back to your
car which is at grid reference 421909.
To do this you will need to walk on a bearing from point to point
What is that bearing?
Answer 301 degrees
plus 4 = 305
DIRECTION OF TRAVEL
NORTH SIGN
360 DIAL/BEZEL
MAGNETIC NEEDLE
True or false?
1.A compass needle is magnetised?
TRUE
2.The red part of the compass needle points to Earth's magnetic South Pole.
FALSE
3.Since a compass is affected by magnetic fields, it needs to be used
away from iron and steel objects.
TRUE
4.The scale of the compass is 0 to 360 degrees. TRUE
5.The parallel lines inside the dial are known as orienting lines. TRUE
6.Orienting lines help to line up the compass with a globe. TRUE
7.The compass needle is painted two colors (Red - North, White - South.)
TRUE
8. A bearing should be followed by following the “red shed” north indicator and
not the direction line.
FALSE
9. The string can be used to measure distance from the map
TRUE
FALSE
10. The bezel cannot be turned or rotated.
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157.5