Help clean up this simple DAX calculation

A few thoughts and a question.

• In your initial COUNTROWS you'd be better just to directly COUNTROWS of the table returned from the filter.
• You can make your code a lot more readable by using variables and formatting it.

Those combined would give:

PctInRange = 
VAR tblGroupAInRange = 
    FILTER(
        Table1, 
        (Table1[Value] < Table1[RangeLow] || Table1[Value] > Table1[RangeHigh]) 
        && Table1[Category] = "A")

VAR cntGroupAInRange = COUNTROWS ( tblGroupAInRange )
VAR cntGroupA = 
    CALCULATE(
        COUNTROWS ( Table1 ), 
        Table1[Category] = "A"
    )

VAR Result = 1 - DIVIDE ( cntGroupAInRange, cntGroupA)
RETURN Result

In terms of making it more dynamic depending on how you're intending to use the measure you could just get rid of the hard coded category = A filters. Sliceing on category would pass the filter straight into both.

Lastly are the high/low values the same for all of category A? If so moving them out to a category dimension might help further.

Share a little on how you'd like to use the measure and we can take it further.