The desired by you functionality of RadPivotGrid is curretnly not provided out of the box. However, you could try to implement and build it by your own - we could assist you in case you face an issues during your implementation.
So, basically you would need to have an initially prepared CalculatedField class that should contain all of the desired RequiredFuields (for your scenario A, B and C). Next, using your UI (you could use a ListBox for example) you need to select the desired fields. Using these selected fields you need to implement your custom logic inside the CalculatedFields class and extract and return the needed expression as DoubleAggregateValue:
DoubleAggregateValue(a * b);
We hope this will help you as a start point for achieving the desired functionality. If you have any further questions or concerns, please let us know.
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