Magnetic Declination

Not understanding the difference between 'true north' and 'magnetic north' can make it difficult to accurately navigate using a map and compass. This difference is known as magnetic declination, sometimes called magnetic difference or magnetic variation.

With this video, I hope to explain what magnetic declination is and how to set your compass correctly so you will arrive at your destination more accurately.

To watch my video on basic navigation:

To watch my video about backstops:

The website I use to determine declination:

The app I use to determine declination:

To learn more about the movement of the magnetic north pole:

#BackPackHack #Magnetic #Declination

[TyJee]

An interesting and fun way of explaining magnetic declination.

To emphasize why mag declination needs to be accounted for in a different way. These ballpark numbers may be helpful to understand why it is important.

A 1 degree error in your bearing will put you off course about 100 ft after traveling 1 mile. (actually about 92 ft, but 100 is easier to remember).

Assuming your bearing was followed precisely, which probably is not possible. Maybe within about 5˚ is about as accurate as most people can walk a bearing. And people should remember compasses are not 100% accurate. I think the Suunto MC2 is specified to have a needle accurate to 2˚. And if you have 10 people sight a bearing, you will probably get 10 different answers. Skill in reading accurately also plays a part in accumulated errors.

The distance off course is approximately = tan (degrees error) x distance traveled.

From your example of ~8˚ east magnetic declination and going to a destination 9 miles away.
tan 8˚ x 9 miles = 1.26 miles, or 2, 226 yards, 6, 678 ft.
[or if using the ball park numbers in the preceding paragraph, 100ft/deg x 8 degrees x 9 miles = 7200ft, but using 92ft/deg would = 6, 624 ft, a little closer to the result using tan 8˚ formula ]

By not accounting for 8˚ east mag declination, you could end up being that distance to far south of where you wanted to go.
(because if a grid north (aka true north) referenced bearing measured on the map is 50˚ it needs to be adjusted to 50˚ - 8˚ = 42˚ magnetic bearing for the correct bearing to follow. Leaving the compass set to 50˚ would guide you to far south) But if following a 42˚ bearing, I think you can see, it would guide you farther north.

And of course if your magnetic declination was instead 8˚ west, and you did not adjust your compass for it, you would end up about 6, 678 ft to far north by following the 50˚ bearing, because you should have set the compass to 50˚ + 8˚ = 58˚. I think you can see following a 50˚ bearing would guide you to far north. And following a 58˚ bearing would guide you farther south.

I will check out your other videos. Should be fun.

[charlesadamski_]

A tiny bit off on this one.
Deviation is actually a local error.
For example - Your fridge motor pulls your compass needle towards it.
It is off a different amount depending on the direction you are travelling and you need to have a list or a piece of paper you can set your compass on that shows that deviation amount for the North south east and west.
That is because - let us say your fridge is in front of your compass.
If you are heading North it will be working with magnetic North.
If you are heading east it will be trying to combat magnetic North by pulling the needle east, etc.
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I know how to calculate it on a ship or boat but not on land yet.
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On charts there are lights set up on the land.
They are marked so that if you line them up to look like one light - this is the degree you are heading.
We simply head towards it and write down the compass reading.
How far does that differ from what the accurate chart says?
Then we head away from it and do the same.
Then we put it on our left and do the same.
Then we put it on the right and do the same.
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I suppose you could do the same on land by putting 2 lights and maneuvering your vehicle.
It's best to do it with your lights very far apart though.
I would guess they'd be a mile apart for navigational charts to ensure accuracy
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Obviously deviation only affects hikers by things like their knives, watches, how far You're standing from that big electrical transformer, etc.
Usually solved by moving away from big metal stuff and holding your arms far out when taking bearings.
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It does affect your motorized vehicles though but It's a constant, It never changes.
( Unless of course you move your motor from the front to the back Or like to plunk your big toolbox beside the compass - Lol)