Measure for Index Starting at One Based on Slicer Selection

[Whitewater100]

Hello PBI Community: 

I am looking for assistance to evelope a measure that would have an index column in a table visual, always start with one, based on a slicer selection. I have provided a sample file and desired results. Thank in advance for any input on this measure. 

Please see attached. Thank you!https://drive.google.com/file/d/1nqTERC3Hdhng7vxtvlhXgmCdJT40rSFU/view?usp=share_link 

[ThxAlot]

Idx = 
CALCULATE(
    DISTINCTCOUNT( 'Table'[ID] ),
    'Table'[index] <= MAX( 'Table'[Index] ),
    ALLSELECTED()
)

[Whitewater100 · Accepted solution]

Hi ThxAlot: That worked fantastic on my example. Thank you very much. I'll accept as the solution. 
What is strange is when I apply the measure to my real data it counts the total number of ID's. Maybe I can try reproducing a table similiar to what I have. But you solved what was asked. Thank you!