>> The amount of fuzz is varied continuously, but the U.S. military knows what
>> it is and can therefore correct for it for their uses.

Don Baccus wrote:

>Close. The extra bits are encrypted, and domestic units aren't
>equipped with the key.
>
>However, some - perhaps higher-end, non portables? - triangulate
>between several satellite readings, and compute a more accurate
>position.

Ummm... I don't want to get into a pissing match here, but all GPS units
triangulate; see Tully's original post about $200 units that track 10 or
more satellites. And since the signals of all the satellites are distorted,
more triangulation doesn't translate into better accuracy on the ground.
More expensive units are more accurate, but the military induced fuzz is
the same for all (i.e. about 100m).

What some commercial users have done to get around this is to set up two
GPS units; one is at a known location/elevation, so the amount of
distortion can be determined. The information recorded by that one is then
used to correct the information collected by the other unit in the field.

Anyway, while this thread is interesting to me, it is a bit off the subject
of birds. I hope we haven't offended anyone by going on about this...

Rob Saecker
Olympia