Onwa Marine Electronics KR-12X8 - Manual (Page 82)

Past Position Display
The past position display shows equally time-spaced dots marking past
positions of activated AIS targets. A new dot is added at preset time intervals
until the preset number is reached. If a target changes its speed, the spacing
will be uneven. If it changes course, its plotted course will not be a straight
line.
Below are sample past position displays.
(a) Ship turning (B) Ship turning
Straight
(c) Ship reduced (d) Ship increased
speed speed
Figure 9 Sample past position displays
Past position plot interval
Enter AIS menu, select "History" t o s elect p lot in terval d esired: O ff,
15s, 30s, 1, 2, 3 or 6 min. Select OFF to erase all past position points and
turn off the past position display.
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AIS Collision Alarm (CPA, TCPA)
The AIS continuously monitors the predicted range at the Closest Point of
Approach (CPA) and predicted time to CPA (TCPA) of each AIS target.
When the predicted CPA of an AIS target becomes smaller than a preset
CPA range and its predicted TCPA less than a preset TCPA limit, the audio
alarm sounds and the symbol of the offending AIS target becomes red,
bold 2 times and flashes together with its vector.
CPA/TCPA alarm ranges must be set up properly taking into consideration
the size, tonnage, speed, turning performance and other characteristics of
own ship.