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# Magnetic declination calculation based on WMM2015 earth magnetism mo
+del.
# See https://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml
...
# $yr: year, default=2015
# Returns magnetic declination for the given location in degrees.
# In array context, also returns magnetic inclination (dip).

BEGIN {
my @WMM2015 = (
...
   my $incl = atan2($Z, sqrt($X*$X + $Y*$Y)) / $DEG2RAD;
   return ($decl, $incl);
}}