Applying Measure after Multiple Selection

Hi , Palmtop 

According to your description, you want to update the [Forcast] measure to meet the "Applying Measure after Multiple Selection". Right?

Here are the steps you can refer to :

I download you .pbix file and test in  my side , you can create a measure to replace your [Forcast] measure:

Forecast2 = 
// Finds latest sales date
VAR EvalDate =
    CALCULATE(
        MAX ( SalesActual[Date] ),
        ALLSELECTED ( SalesActual )
    )
var BoundaryDate = EOMONTH( TODAY(), -2 ) + 1
VAR Date_ =
    // If latest sales date is older than 2 months, 
    // it will default back to current month.
    IF ( EvalDate < BoundaryDate, 
        BoundaryDate,
        EvalDate
    )
var _id = VALUES('Product'[Product])
VAR SalesHistorical = 
    CALCULATE(
        [Actual Sales],
        'Calendar'[Date] = Date_,
        SalesHighLow[Product] in _id
    )
VAR SalesHigh =
    CALCULATE (
        // Value of sales high curve @ Date_
        [High Sales],
        'Calendar'[Date] = Date_,
        SalesHighLow[Product] in _id
    )
VAR SalesLow =
    CALCULATE (
        // Value of sales low curve @ Date_
        [Low Sales],
        'Calendar'[Date] = Date_,
        SalesHighLow[Product] in _id
    )

var _cat = SWITCH(
                TRUE(),
                SalesHistorical <= SalesLow, 1,
                SalesHistorical <= SalesHigh, 2,
                SalesHistorical >= SalesHigh, 3
                )

var _result = IF ( MIN('Calendar'[Date]) >= Date_, 
    SWITCH ( 
    TRUE(),   // TRUE used as first argument allows SWITCH to replace nested IFs  Cleaner to read. 
    _cat = 1, CALCULATE( [Low Sales] * DIVIDE(SalesHistorical, SalesLow) ),
    _cat = 2, CALCULATE( ( [High Sales] * (SalesHistorical - SalesLow) + [Low Sales] * (SalesHigh - SalesHistorical) ) / (SalesHigh - SalesLow) ) ,
    _cat = 3, CALCULATE( [High Sales] * (SalesHistorical/ SalesHigh) ) 
    )
)

return
    _result

And then we will meet your need:

Thank you for your time and sharing, and thank you for your support and understanding of PowerBI! 

Best Regards,

Aniya Zhang

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