There is no "information stored in the sub summary". But you can calculate the same sub total--either with a self join relationship or in a calculation field using the GetSummary function.
Thanks for the reply.
I have a calculation field using the get summary function. The issue I have is that I have the sub summary driven by the VAT rate, so when I click in one of the tables, the calculation changes due to being driven by the VAT rate.
In Browse mode I have both totals showing based on the VAT rate applied.
GetSummary returns a value based on the records in a found set and how they are sorted, but a relationship can match to a specific set of records, such as line items linked to the current invoice and then an aggregate function such as Sum can compute a total. That relationship can be set up to match to only certain line items--those that contribute to the total needed for your tax calculation, for example.
Beyond that, there's not enough detail in what you describe for me to provide any more assistance. I'd need to know more about the design of your database table(s) before I could suggest anything in more detail.