Crystal Reports uses a parameter field mechanism for linking subreports to main reports.
When linking a main report field that is not a parameter field to a subreport field, the program:
Automatically creates a parameter field to complete the link.
Modifies the subreport record selection formula to select those records in which the subreport field is equal to the parameter field value.
The need for a parameter field is implied; it is called an "Implicit Link" situation.
At times, you may wish to use a linked parameter field in a subreport without using it as part of the selection formula for the subreport. For instance, you may want the main report to pass in a summary value that can be used in calculations by the subreport, or you may want the main report to pass in the title of the subreport.
When you link a field in the main report to a parameter field that you have created in the subreport, the program:
Checks the link you have specified.
Does not create any additional parameter fields.
Does not modify the subreport record selection formula.
Specifying a link is called an "Explicit Link" situation.