Filter _ slicer _ line chart

Hi Anonymous 

Calculated columns aren't dynamic in Power BI.  That is, slicer selections do not affect the values in them as they are not recalculated.

Measures are dynamic, so that's what to use.

Here's a measure to get the values.  You may want to think about what value should be displayed at the total level.  That isn't specified in your question

incident per period value = 
VAR _MileagePerPeriod = 
ADDCOLUMNS(
    SUMMARIZE(
        Incidents,
        Incidents[Period],
        Incidents[ Mileage per period]
    ),
    "@Rows", CALCULATE(COUNTROWS(Incidents))
)
VAR _Result = SUMX(_MileagePerPeriod, DIVIDE(Incidents[ Mileage per period], [@Rows]) )
RETURN
    _Result