hmmm.. it used to be (pre 1970s) that you could approximate the change in
deviation by 1/2 degree per decade (in California). But now that the
magnetic north pole seems to be moving quite rapidly (40 km/yr) it could be
changing pretty quickly. Worst casing, for 33 degrees latitude (6000 km
from pole) and movement directly normal, the change would be on the order
of 40/6000 radian = .3 degree/yr.. a whole bunch...
I wonder if the etrex has a command to set this?
At 08:50 AM 2/13/2003 -0800, Michael Tope wrote:
>Jim, et al:
> >From the looks of it, the Garmin unit is nothing more
>than standard GPS handheld with a built-in flux gate
>compass (note that compass accuracy degrades
>significantly in extreme northern and southern
>latitudes suggesting a dependence on the earth's
>The advantage appears to be that unit automatically
>performs the "true north" correction based upon the
>GPS position data. Compass accuracy is specified to
>depend upon calibration, so you probably have to
>update the coordinates for the magnetic north pole
>occasionally. Seems like a good idea (one less thing
>to think about on the tower).
>73 de Mike, W4EF....................
> > The GPS receiver doesn't measure any bearings... it measures distance to
> > satellites, and does "tri-lateration" not "tri-angulation"
>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
>any questions and ask for Sherman, W2FLA.
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