Display total value on subform

[CW]

I have a job-costing page for our orders, which is a subform on a tab control
linked to all other parts of the database by Ref.
The aim is to show all costs, with total, then all revenue, with total, then
the profit.
The incoming costs are entered here and then stored in a table, no problem.
Sales invoices are generated via other forms and I have a query that
displays just the basic details for each invoice filtered by Ref so that we
see only the invoices raised for that particular current order. These are
displayed on a nested subform based on the query.
When there are several sales invoices for the job, I need to show the total
revenue (and then use that to calculate the profit).
Given that a sum cannot be produced within a query, how can I do this?
Thanks
CW

 

[Beetle]

You can put an unbound text box in the footer of the subform an use it to
total the records in the subform.