When adding conditional formatting or other constraints on data-driven report elements, you have the option of using a built-in Formula Editor to help you build an expression with a graphical interface. All element properties in Report Designer can have formulas. You can type in your own formula by hand, but it's much easier to use the built-in Formula Editor to build an expression.
The Formula Editor provides you with basic math and comparison operators so that you don't have to enter them manually. Also provided are concatenate and percent functions. Click the Field Selector to select fields in the report.
Follow the instructions below to use Formula Editor:
You have applied a formula to a report element.
Note: If you want more information on formula functions, conditionals, and operators, refer to the OASIS OpenFormula reference: http://www.oasis-open.org/committees/download.php/16826/openformula-spec-20060221.html. Pentaho does not implement all OpenFormula functions, but the functions Report Designer includes are documented on the OASIS website.