> Why forget it if it is a compas? I (apparently incorrectly) assumed that a > compas *would* be sensitive. If you take a standard marine chart and want to > plot a course based on a bearing then you may or may not be taking magnetic > declination into account (ie, true north vs magnetic north). In NZ, although > the variance is only 2-3 degrees accross the country, the declination itself > ranges from about 21 to 23 degrees.
You are wondering though whether its worth getting a total field map for NZ (which is a raster not a conveniently calculated spherical harmonic because it reflects the crustal geology) instead of just using the numbers from the IGRF. I am contending that you couldn't detect the difference between the IGRF model and actual field with a compass. Its not a precise enough instument. ---------------------------------------------------------- Phil Scadden, Institute of Geological and Nuclear Sciences 764 Cumberland St, Private Bag 1930, Dunedin, New Zealand Ph +64 3 4799663, fax +64 3 477 5232 _______________________________________________ Delphi mailing list [EMAIL PROTECTED] http://ns3.123.co.nz/mailman/listinfo/delphi
