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Re: Annual Increase of Variation
From: Steven Wepster
Date: 2002 Feb 12, 14:11 +0100
From: Steven Wepster
Date: 2002 Feb 12, 14:11 +0100
>What is the cause of the "annual" portion of the magnetic variation on >the compass rose? The earth's magnetic field is not constant but subject to ... well, variation. The annual correction is a local linear approximation to the change. As such it is not valid for ever; its value should be revised after some time on the basis of regular determinations of the variation. If the annual change is given as 1' -- 3' then after 20 to 60 years the variation has changed 1 degree. I don't know the policy of the hydrographic office: whether they update the compass rose only at new editions of a chart or also at reprints. If the former applies, and no new edition has occured in 20 years, then you don't see a change in variation on the chart. _Steven. ----------------------------------------------------------- Steven Wepster wepster@math.uu.nl tel +31 30 253 1186 Mathematisch Instituut Universiteit Utrecht PO Box 80.010 3508 TA Utrecht The Netherlands ===========================================================