Nested set expression in Qliview/Qlik sense

This project is about a modelling problem in which I need an expert in qlikview/qliksense. I currently have a table in which I have store and item as a dimension. For this table I have 3 columns: "Last inventory date", "second to last inventory date" and "Inventory value" which is calculated as the inventory value between the dates in the previous column. The issue I have is that while the dates are calculated correctly, the inventory value is wrong. I suspect that it is because each row has different dates to consider, but I have no time to confirm this. This should be a simple task for a qlikview expert so please only bid if you are confident in qlikview/qlik sense.