RB aggregate fields

I have a job costing report that compares sales to actual costs and am grouping it by jobcode, reset page, repeat header, with aggregate fields for jobcosts and for selling price. I would like to get a ratio or percent on the same line or for each group for the aggregate fields costs / sell price. When I make a calculated field to do this I get a error saying cannot calculate circular references. Is there a way around this?
any help would be appreciated.

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