You can choose to use either the Actual Port Cost or Preliminary Port Cost of previous port calls to update the port cost of the selected port call.
To make use of a Preliminary Port Cost of a previous port call, click the button to the right of the Preliminary column. To make use of an Actual Port Cost of a previous port call, click the button to the right of the Actual column. Clicking this button will also update the currency of the port cost of the selected port call to the currency shown on the row.