Compass
What does the red end of a compass needle point towards?
Magnetic North.
What are grid references used for?
To show the location of a place or point on a map.
What does it mean to orient a map?
To turn the map so its north and features match the ground around you.
What is a bearing?
A direction measured clockwise from north, usually in degrees or mils.
What is a navigation data sheet used for?
To record important route information and help navigators plan and track their movement.
Why should a compass be held flat and level?
So the magnetic needle can move freely and give an accurate reading.
Which do you read first: eastings or northings?
Eastings first, then northings, “along the corridor, up the stairs.”
What are the three north points used in navigation?
True North, Grid North and Magnetic North.
How many degrees and mils are in a full circle?
360 degrees or 6400 mils.
What is a “leg” on a navigation data sheet?
One section of a route between two locations or checkpoints.
Name four important parts of a Silva compass.
Baseplate, magnetic needle, rotating housing and direction-of-travel arrow.
What is the difference between a four-figure and six-figure grid reference?
A four-figure reference identifies a grid square, while a six-figure reference identifies a more precise point inside it.
What is the difference between Grid North and Magnetic North?
Grid North follows the map’s vertical grid lines, while Magnetic North is the direction shown by a compass needle.
What is the difference between a grid bearing and a magnetic bearing?
A grid bearing is measured from Grid North on a map, while a magnetic bearing is measured from Magnetic North using a compass.
Name five details recorded for each leg.
Start and destination, distance, grid bearing, magnetic bearing and estimated time.
How do you measure a grid bearing using a Silva compass and map?
Place the compass edge from the starting point to the destination, point the direction arrow towards the destination, rotate the housing until its orienting lines are parallel with the map’s grid lines, then read the bearing at the index line.
What tool can help you accurately measure a six-figure grid reference?
A roamer, which divides the grid square into tenths.
How do you orient a map using a compass?
Place the map flat, identify Grid North, hold the compass level and rotate the map and compass together until north agrees.
How do you measure a grid bearing using a Silva compass?
Place the compass edge from the starting point to the destination, point the direction arrow towards the destination, rotate the housing until the orienting lines match the map’s grid lines, then read the bearing at the index line.
Why should navigators record both distance and estimated time?
Time can be used to check whether the team has travelled approximately the correct distance.
A cadet’s compass gives an unexpected reading near a vehicle. What is probably causing it, and what should they do?
The vehicle’s metal may be interfering with the compass. The cadet should move away from the vehicle, hold the compass level and take the bearing again.
Explain how to obtain a six-figure grid reference.
Find the grid square, read the easting to the left and estimate the tenths across, then read the northing below and estimate the tenths up. Combine them as three easting digits followed by three northing digits.
Why must navigators understand the difference between north points?
Maps use Grid North while compasses point towards Magnetic North. The difference between them must be considered when converting and following bearings accurately.
Why must a grid bearing be converted before being followed in the field?
A map uses Grid North, but a compass points towards Magnetic North. The bearing must be converted using the current map’s Grid Magnetic Angle so it can be followed accurately.
Why might the actual travel time be longer than the estimate?
Rough terrain, vegetation, darkness, equipment loads, obstacles or extreme weather can slow the team’s movement.