To see an example of using an exception in a variable, review correlated_subquery.srm in the Samples folder. The default path for this srm file is: ..\Hyperion\products\biplus\bin\SQR\Studio\Samples. If you placed SQR Production Reporting Studio in a destination other than the default destination, then look for the Samples folder and report there.
In the example, "correlated_subquery.srm", the exception is on the report field "ExceedsAverageSalaryBy". If the difference between the employee's salary and the average salary for their region is greater than $1000, that amount is highlighted in blue in the finished report.