A magnetic compass needle’s movement is based upon the
earth’s magnetic field. That magnetic
field and the movement of the magnetic needle on its pivot point in part, determine
direction.
Ideally, there is no interference from any objects.
But that is not reality.
Nickel near the earth’s surface, rifle barrels and power lines all interfere
with the compass’ movement. What are the
standoff distances that the hiker need observe?
I went to two publications to get that answer. Camping
and Wilderness Survival by Paul Tawrell (page 177) and GPS Land Navigation by Michael Ferguson (page 53) became my sources.
Metal
Object
|
Ferguson
|
Tawrell
|
Power Lines
|
55-60 meters
|
55 meters
|
Truck/Car
|
18-20 meters
|
10 meters
|
Telephone wires/barbed wire
|
8-10 meters
|
10 meters
|
Rifle/hand tools
|
2-3 meters
|
-
|
Pocket knife/binoculars/electronics
|
½ - 1 meter
|
-
|
Shovel
|
2-3 meters
|
½ meter
|
Interesting data points to consider. For example, if you combine the bottom three
rows of information it becomes common sense to ensure the hiker’s gear is out
of the way.
Neither reference identifies the amount of impact these objects will have on the compass needle. That is not practical for the average hiker. It is the hiker's movement away from the object (.e.g., fence or car) to mitigate the error induced.
Neither reference identifies the amount of impact these objects will have on the compass needle. That is not practical for the average hiker. It is the hiker's movement away from the object (.e.g., fence or car) to mitigate the error induced.
I would also offer that one should be careful how close
to a compass electronics are stored in a pack.
I’d just keep it simple by stowing the flash light, GPS receiver and
camera in a pack pocket/compartment away from the compass.
Note that GPS manufacturer Garmin recommends moving away
from metal objects when calibrating the GPS receiver’s electronic compass.
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