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I wrote:

> back to Dave's original question,
>
> > What sources exist to determine compass variation for your position at
> sea?
>
> what counts as fair for sources?  variation is printed on every chart,
> right?  world maps are available (in APN for example), GPS has it built
in.
> given most variations are just a few arc minutes you would need a flat
calm
> but sights on polaris might do it, good luck though.

(never mind arc-minutes, brane faide there!)

here's the polaris idea, without sights.

align a reference object (such as mast of boat, or forestay) with polaris.
assuming the boat's compass is swung correctly (deviation known and possibly
corrected) and aligned correctly with the reference object, note the compass
reading, that's the local variation +/- 1o.  obviously the further away the
reference object and the compass are the better this will work.

Cliff

   

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