Why does -1, -1, and 2 equal 4 in a pivot table
 

Trying to do a pivot table to calculate processing time using Beginning
Inventory + Received - Ending Inventory. Used formulas to 'Reverse' Ending
inventory thinking I could do a Pivot table on the results however the Pivots
appear to be using the absolute values. Confirmed this using Drill down to
review the data and the values are no longer showing the negative signs.