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For you guys who do not have Differential GPS Good news.
#1
: Effective at Midnight (GMT) on May 1, 2000, the Selective Availability
(SA)
: degradation feature of the Global Positioning System was discontinued.
The
: result is that the position and velocity information provided by GPS
: receivers is now up to 10 times more accurate than before the
discontinuation
: of SA.  No adjustments or upgrades to GPS receivers are required to take
: advantage of the improved accuracy.
:
: Selective Availability (SA) is the deliberate introduction of error to the
: precise timekeeping of the GPS satellites, thereby reducing both
positioning
: and timing accuracy for civilian users.  It was designed to provide US and
: Allied military forces with a navigational advantage in times of crisis or
: conflict.
:
: This news is of particular importance to mariners, as the discontinuation
of
: Selective Availability (SA) will improve the predicted accuracy of GPS for
: civilian users from within 100 meters (about 300 feet) to within 20 meters
: (about 60 feet).  In many cases, real-world users will find the accuracy
to
: be even better.
:
: Users of Differential GPS (DGPS), an error correction add-on to
stand-alone
: GPS, have already been enjoying positional accuracy in the 1 - 3 meter
range,
: so the discontinuation of SA will have little effect for those users.
: However, the difference in accuracy between stand-alone GPS and DGPS has
now
: been significantly reduced.
:
: Additional information on GPS can be found at the Interagency GPS
Executive
: Board web site at <A HREF="http://www.igeb.gov/">www.igeb.gov</A>.

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