
ARPA - ACCURACY AND ERRORS
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of 110°(T), target a has appeared on the starboard bow.
By transferring line Oa so that a lies on the indexing
target at A, it is established that the target is well outside
the fairway at O
t
and the observing vessel expects to
turn to 020°(T) before reaching the target.
Where ARPA facilities are provided, it should be pos-
sible to extract collision-avoidance data in the usual way.
8.4.8.2 Using a
true-motion ground-stabilized presentation
(a) Without ARPA. Moving targets within the vicinity
are soon recognised after a small amount of plotting
on the reflection plotter. Their positions and
approximate movement ...