unique(?) calculation on each row of a list

[Quartekoen]

I have a table that lists the basic details of all the invoices for a certain customer. Basically, I have a column for the date, charges, credits, and the running total. What I need is for that running total to update on each line based on the previous total + charges - credits, but in list view, I'm not sure how to set up the field to reference a previous version of itself. Any help would be greatly appreciated. Thanks.

[Fitch]

GetNthRecord( total ; Get(RecordNumber)- 1)