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Old 01-29-2014
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Re: Magnetic Variance

Quote:
Originally Posted by Dean101 View Post
The examples I'm looking at show the compass rose of a chart with the variance noted in the center. I was hoping that following the rule of add east, subtract west will work on any chart.
Charts for the west coast will have an easterly variation noted in the middle of the compass rose. Charts for the east coast will have a westerly variation. They aren't interchangeable in the way I think you mean. If you're using a chart for say, the entrance to New York Harbor, you'll use the westerly variation as noted in the compass rose.

They give you both east and west so that the publishers can use the same example on either coast. But you need to use the one that's applicable to your area.

Quote:
Originally Posted by Dean101 View Post
Another question; When the rose has an inner magnetic rose, it is drawn to the variance noted in the center for that year, right?
Yes.

Quote:
Originally Posted by Dean101 View Post
If the chart is older and the variance over the years was great enough to change the degree variance, I'll still have to allow for that if I use the inner magnetic rose.

Thanks for the response by the way.
You'll have to account for the change in variation over the years regardless of which direction you are going (magnetic to true or true to magnetic).

I hope this helps.

A great book that I recommend is How to Read a Nautical Chart by Nigel Calder. Good explanations and it also contains all of Chart No. 1.
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