Calculating a rolling difference over integer categories

That's page 198 of my book, Crafting a funnel drop-off rate, it goes something along the lines of:

Drop Off Rate = 
    VAR __CurrentStep = MAX([Step])
    VAR __PreviousStep = __CurrentStep - 1
    VAR __CurrentCount = COUNTROWS('R01_Table')
    VAR __PreviousCount = 
        IF(
            __CurrentStep = 1 , 
            0 , 
            COUNTROWS(FILTER(ALL('R01_Table'),[Step] = __PreviousStep ))
        )
RETURN
    DIVIDE(__CurrentCount - __PreviousCount, __PreviousCount, 0)

There is also Abandoment Rate:

Abandonment Rate = 
    VAR __CurrentStep = MAX([Step])
    VAR __PreviousStep = 1
    VAR __CurrentCount = COUNTROWS('R01_Table')
    VAR __PreviousCount = 
        COUNTROWS(FILTER(ALL('R01_Table'),[Step] = __PreviousStep ))
RETURN
    DIVIDE(__CurrentCount - __PreviousCount, __PreviousCount, 0)

Hi Anonymous ,

You wanna calculate the differences in steps,right?

Then use below dax expression to create a measure:

Measure = 
var a =CALCULATE(MAX('Table'[Unique customers]),FILTER(ALL('Table'),'Table'[step number ]=MAX('Table'[step number ])-1))
Return
DIVIDE(MAX('Table'[Unique customers])-a,a)+0

And you will see:

For the related .pbix file,pls click here.