Online tool for Mag Dec info

Blake

Nest In the Hills
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Thanks Redtail!

Ive been looking for something like this!

Checking Mudgee it says the dec is 11.554 changing -0.0126 per year. My 2006 topo map says its 11.7 changing less than 0.00 degrees per year. So pretty good but which is right?

Mag dec angle is the angle between true north and magnetic north so its Grid-magnetic Angle - Grid Convergence Angle right? Why dont they print this on maps? All my maps have the grid convergence angle and the grid-magnetic angle only. Why dont they have all three? Is it to eliminate error because only the MN angle is the one that changes? Just a question.
 
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Redtail

Richard Proenneke
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Checking Mudgee it says the dec is 11.554 changing -0.0126 per year. My 2006 topo map says its 11.7 changing less than 0.00 degrees per year. So pretty good but which is right?
The short, practical answer is - I would say - it doesn't matter. One is a live model, the other would have been modelled on best data available over a certain time period. 11.554 rounds to 11.6 (compare with 11.7, i.e. 0.1 deg), and the dial on most compassess is only accurate to 0.5 deg in the first instance. ... Thinking back to my engineering days when the introduced error of any gauge is 1/2 of its smallest marked gradation. Assuming most compasses are only marked to 1 degree, error is 0.5 degree. Of course, if it's marked down to half degrees, then you're looking at an error of 0.25 degrees, but that's still 2.5 times the 0.1 difference we started with above. Then factor in your cross-checking with landmarks, tracks, landscape, etc, you'll know where you are, for all intents and purposes.

But you'd probably need to ask a cartographer for a more detailed answer.

Mag dec angle is the angle between true north and magnetic north so its Grid-magnetic Angle - Grid Convergence Angle right? Why dont they print this on maps? All my maps have the grid convergence angle and the grid-magnetic angle only. Why dont they have all three? Is it to eliminate error because only the MN angle is the one that changes? Just a question.
Some of my maps do have all three. But here in the west, mag dec is usually less than 2 degrees. So by the time I factor in all of the above, most places I walk, it makes very little difference. Obviously, if I was travelling some distance over flat country (or in the east), I'd have to take a lot more care! Or a sextant/octant.
 
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