Calculations based on a specific value in the range

[Chmielo]

Hi,
I need to create a column based on the difference from column "Value", and the average value of the date range given in slicer. For example:
Actual Table

Date	Value
2021-01-01	5
2021-01-02	10
2021-01-03	15
2021-01-04	20

In the slicer we selected the date range from '2021-01-01' to '2021-01-03' - The average for this interval is 10. My main problem is that I cannot use this value as a 'constant' (as in excel by using $). The new column should look like this:

Date	Value	New Col
2021-01-01	5	(5-10)^2
2021-01-02	10	(10-10)^2
2021-01-03	15	(15-10)^2
2021-01-04	20	?BLANK()? OR (20-10)^2 (but its important that the average is only calculated from the slicer)

If we select another day in the slicer, the average is 12.5 and a new column should be calculated based on this value. For first day (5-12,5)^2 etc. I tried something like this but without any positive result:

x = AVERAGEX('TABLE',POWER('TABLE'[Value]-(CALCULATE(AVERAGE('TABLE'[Value]),DATESBETWEEN('Calendar Table'[Date],MIN('Calendar Table'[Date]),MAX('Calendar Table'[Date])))),2)) - Date from Calendar Table is used in the slicer. 

[Fowmy · Accepted solution]

@Chmielo 

You can create a measure for this because a calculated column cannot access the values selected in the slicer. 

New Value = 

var _avg = CALCULATE( AVERAGE(Table1[Value]), ALLSELECTED(Table1[Date]) )
var _value = 
    AVERAGEX(
        Table1,
        (Table1[Value] - _avg ) ^ 2
    )

return
    _value