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I use the simple "True virgins make dull company approach" when navigating
Where true is "True"
Virgins is "Variation"
Make is "Magnetic"
Dull is "Deviation" which dont count, based on JimmyH's post.
Company is "Compass"
Working from left to right in this equation using Var east compass least etc.
You get the correct result. of course the whole equation can be reversed to go the other way.. On a nautical chart the info for var is in the compass rose, the year the chart was printed with the amount to add for every subsequent year. usually several roses all slightly different placed appropriately on the chart, the differences on a large scale chart are very small. local anomolies often are the consideration. And deviation as per above is not to be ruled out, unless you are out in the middle of a paddock somwhere, you would be supprised by what upsets a good compass...
This is info gleamed from my 5 years of sailing the south pacific...
hope it helps.
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