Using Formula Fields without Linking
Formula fields can also be used by a subreport without linking them. This is used when you want to pass data to a subreport without filtering the data. For example, the main report can pass a string to the subreport so that the string gets printed in the subreport’s header.
Passing Data Via Shared Variables
Shared variables let you share data between a main report and its subreports. This lets you perform calculations, track subtotals and create strings in one report and pass this data to the other report.