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Select the Detailing to Expense Item option to indicate to the system that the proportions will be specified per each expense item, that is, the cost associated with each listed expense item will be splitted split between multiple Cost Objects.
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If you need to manually add a cost or expense, click the Add button.
Use the Up and Down ( 
) buttons to rearrange the expense items in the list.
Click the Split Row ( 
) button to copy the selected cost (row). Then you can split the expense item costs between multiple Cost Objects.