Lowrance HDS Live Operator's Manual page 159

For information about extension lines for your own vessel, refer to
"Extension lines" on page 49.
Defining dangerous vessels
You can use the CPA (Closest point of approach) and TCPA (Time to
closest point of approach) values to define when a target should be
considered as dangerous. When a target comes within the distance
for CPA or within the time limit for TCPA, the symbol changes to the
dangerous target symbol.
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AIS| HDS Live Operator Manual