Moving Range DAX (subtract previous row values from earlier DateTime)

Hi Zubair_Muhammad, 

1) Wrap a "ISBLANK" around MovingRange, such that the Moving Range for 1st row is blank(). 

MovingRange = 
IF(ISBLANK(data1[EarlierTime]);blank();(
VAR EarlierTime = CALCULATE ( MAX ( data1[TimeSPC] ); FILTER ( ALLSELECTED ( data1[TimeSPC] ); data1[TimeSPC] < SELECTEDVALUE ( data1[TimeSPC] ) ) ) 
VAR EarlierMeasureValue = CALCULATE ( SUM ( data1[MeasureValue] ); data1[TimeSPC] = EarlierTime ) 
RETURN ABS ( EarlierMeasureValue - SUM ( data1[MeasureValue] ) ) ))

2) Que: Can advise the DAX for Average of Moving Range (ie. MRbar)?

3) To correct myself, my goal is to calculate the sigma value = MRbar/1.128 (not Cpk and 1.128 is a constant). 

https://1drv.ms/u/s!ArjVwEnHONXNghx02BIdTGGtSrlZ

Oops, correction. It is the "SELECTEDVALUE" function that is missing from Excel DAX. 

Moving Range =
VAR EarlierTime =
    CALCULATE (
        MAX ( data1[TimeSPC] ),
        FILTER (
            ALLSELECTED ( data1[TimeSPC] ),
            data1[TimeSPC] < SELECTEDVALUE ( data1[TimeSPC] )
        )
    )
VAR EarlierMeasureValue =
    CALCULATE ( SUM ( data1[MeasureValue] ), data1[TimeSPC] = EarlierTime )
RETURN
    ABS ( EarlierMeasureValue - SUM ( data1[MeasureValue] ) )