How To Perform Calculations Over Dimension Items

[mquesada]

Is there a way to perform a calculation over dimension items, lets say two (or more), to create a new one wich would be the result of the operation? For example if I have an item of Incomes and an item of expenses and I want to calculate a balance and show the result as a new item called Balance.

[AlexZencovich]

Create hierarchy item <Balance> with sub items <Income <Expence>. If all expence-related values will with minus and income with plus - balance will show sum of both.