Variance in Pivot Table with multiple columns

[Nolan]

Good Afternoon,

We currently have a pivot table that includes our Actual Sales and various Forecast scenarios for 2020 and 2021. Our Values are the rows and we have 2 column dimensions, Scenario and Year.

We want to create 2 variance columns comparing scenarios: FC0 vs Preliminary Forecast as well as BUD vs FC0.

ex: 

Sum({$<Scenario={'FC0'},[2016-2018.Year] = {"2021"}>}Units)
-
Sum({$<Scenario={'Preliminary Forecast'},[2016-2018.Year] = {"2021"}>}Units)

Is there a way to do this without adding some sort of extension? And if we do need an extension, does anyone have a suggestion? Apologize if a question like this has been answered elsewhere, but I can not find this specific problem.

Thank you for the help.