HANA Calculation of differential amount on the fly

Hi,

I have a scenario where I want to calculate the differential amount between successive rows on the fly..sample structure of my table is like this:

I want to show a new column "Diff." on the fly that would show 0, -20, 60 in the above example.Is there a way I can achieve this without Triggers(while loading) in HANA using calculation views or decision tables? Or can this be done only in the reporting layer?

Thanks,

Anil