The Ship Display feature on the tonnage toolbar provides three options by which to order and view your tonnage list.
'Spot' View
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The 'All positions' view displays all open positions as and when received and parsed from emails. Ships may be displayed several times as no prioritisation or condensing of positions is applied - hence you may (as well as ETA positions) as they are received, and may therefore The Ship Centric view prioritises the most current and closest opening position for each vessel (rather than displaying all potential ETA positions that may be listed in emails).