Using Set Expression for Current month and last month data

[Anonymous]

I am trying to use a set expression to calculate a yield percentage for a KPI for current month and prior month values.

The expression I am trying to use for this is as follows

Sum({1<Line={Line1, Line2, Line3},Process Month={Month(Today())}>} Yield output)

I want the KPI to be fixed for a set number of lines for this month.

Thank you!