Thank you for your reply. The problem is that the derived calculated items are limited. The cashflow in the crosstab is based on a text filter (drop-downlist control) for example 'Q1 2016' and I want to compare this with the cashflows 'Q4-2015' in the same crosstab. So entirely not based on a date. Probably the answer is a calculated data item with something like:
if (previous period = 😎 return cashflow else 0
But then I get when previous period = 8 only the cashflows based on the filter from the drop-downlist.