Crystal Reports for Rational Application Developer Designer Guide
Does the data exist or does it need
to be calculated?
Some report information can be drawn
directly from data fields (sales information, for example); other information
will have to be calculated based on data field values (for example, sales
commission, based on the relationship of sales to quota). In your planning, it
can be helpful to segregate or flag data that needs to be calculated from that
which can be used directly. For more information, see
Specifying formulas.