How to create a calculated measure that calculates the variation between the 1st and the last value of a selection.

[Madeleine]

Hello,

How to create a calculated measure that calculates the variation between the 1st and the last value of a selection.
For example, if we select Feb 2022 and Aug 2022 we want to see Aug 2022 vs Feb 2022., or Feb 2023 vs Feb 2022
I need two columns: in first column to see the values for the first selection and in the second column to see the values for the second selection.

I create a calculated measure for Previous Month and one calculated measure for Current Month, I can select any month from the previous years vs Current Month but I can't select two months from the previous year.
I don't know what to use for the second column, instead of Current Month.

I tried all the functions from Digdash

Thank you,