Listbox with Date - how to calculate month and month-1

[#1]

I have a pivot-table where I calulcate =sum(Value) to see the sum of different dates from a listbox. Now I want to calculate the value of the selected month and the month - 1 or from my listbox the value from selected Item - 1

I tried everything, analysis sets, monthadd and other functions, but I never get a useful result. How can I calculate the sum from the month-1 or even month-2 and so on...

thanks in advance

Thomas

[#2]

PERFECT, this is working great

sum({< DATE = {'$(vDate)'}>} AZ_WERT)

Thank you very much.