NorthStar 951, Operator'S Manual

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Page 28 951/952 Operator’s Manual Rev. B
Chapter 2 - Introducing the Northstar 951/952
GPS provides an absolute accuracy better than 100 feet nearly
everywhere in the world, under virtually any conditions. This
far surpasses the 600-foot absolute accuracy that’s achievable
from a good loran receiver under ideal conditions.
If you’re used to having your Northstar loran’s repeatable
accuracy return you to within a boat length of a lobster trap or
a buoy, time after time, you won’t necessarily see this same
performance with uncorrected GPS—you could be as much as
200 feet from your expected position. This is especially appar-
ent when using the unit’s
CHART
screen, where you can see
your boat’s plotted position appear to wander around within
an area up to 200 feet in diameter (see figure below).
Figure 2: Position accuracy of uncorrected GPS
Increasing position
accuracy
If you need a higher level of repeatable accuracy than what
basic GPS provides, you have two choices:
•
Use DGPS by one of the following options:
>
converting your 951X to a 951XD or your 952X to a
952XD by adding an internal differential receiver
>
adding an external Northstar differential receiver
>
using another source of differential corrections
Using good DGPS corrections, your unit should provide
better than four-meter accuracy (repeatable and absolute)