Using Actuate BIRT Viewers : Functions and operators : DIFFERENCE( )
 
DIFFERENCE( )
Calculates the difference between values in two columns, ColumnB – ColumnA.
Category
Math
Column
In the first field, select a column from the list, or type a value to subtract from the second field.
Column
In the second field, select a column from the list.
Returns
Interactive Viewer subtracts the first value from the second value and displays the difference in the cross tab.