Regarding the IMO requirements for past positions, what can all ARPAs display?

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Past positions on ARPA are shown in two reference frames to give a complete historical view of a target’s movement. The true past positions are the geographic coordinates (lat/long) where the vessel was observed, which lets you track its actual path on the chart. The relative past positions are how that same vessel appeared from your own ship’s perspective (bearing and range), which is essential for interpreting how the target is moving relative to you. IMO requirements require ARPA to display past positions in both forms because this dual view helps you assess past motion and predict future risk of collision. With both true and relative past positions, you can see where the target has been on the chart and how its motion relates to your vessel, providing a complete picture for safe navigation.