I created three fields: A, B and C. A - B = C. So C is the result of a calculation of entered data A and B. 

However, when I create a Pivot table C is displayed as no value. It is not being calculated. In the columns that are dragged into the Pivot table fields, there are two options for data: Dimension and Range. If it is range, the report shows a range and the value is not calculated. If it is Dimension (treated as text), the correct entered values (A, B) are presented but the calculation is not. (See figures below)