Calculated Item to find delta on two data source creates new data sets

Hello all!

I am trying to create a pivot table that compares data from two data sources and i'm using a calculated item to find a delta.
After creating the calculated Item, the Pivottable now creates additional data sets for which the calculated field is running against.
See attached screen shots which show the data set and the pivot table with the calculated item
PIVOT.PNGAttachment 769421

The calculated item is simply = Actual - Planned

Highlighted in yellow are the new data sets that the Pivot has created which don't exist in the Data set.
I've tried using a value filter on the fields, but this makes the excel too slow and almost unusable as my data file is >1000lines long

I know this is do-able, i've seen it done before and used the file. I'm just trying to re-create the analysis.

Any help or suggestions would be appreciated.

Thank you