Pivot Table | Use previous value in calculated item

I would like to create a calculated item based on the previous value in the pivot table.

In my mind the calculated item formula would be: =Col_A - (Col_A[-1] * 100) thus giving the following output:

Col_A = Original Data
Col_B = Delta from previous value times 100

Col_A------Col_B-----
----6------------0--------
----9------------300----
----10----------100-----

Is this possible?

Thanks,
JC

I've tried adding a "Difference From" field to the pivot table, but then I'm not able to use that field in a calculated item.

Any other ideas?