Need help with a dynamic percent change based on selected slicers

[Anonymous]

I need to calculate the percent change between two values based on the selected slicers. I have 4 years of data on my graph (see below), and I'd like to calculate the percent change in price based on the below example. 
This is what my graph currently looks like along with the two slicers. 

I want to be able to select a year and then two months and get a percent change for the two prices, For example, the below would be a -6% change from October to April. 

Below is what I came up with, but haven't been able to make it work. Any input would be greatly appreciated:

% Change ASP_Historical =

 DIVIDE(

    CALCULATE(

        'Historical Sales'[ASP],

        FIRSTDATE('DATETABLE'[Date])),

        CALCULATE(

            'Historical Sales'[ASP],

            LASTDATE('DATETABLE'[Date]))

            -1)

[Fowmy · Accepted solution]

@Anonymous 

Try this measure please:

% Change ASP_Historical = 
VAR __MinDateValue = 
    CALCULATE(
        [ASP],
        FORMAT('DATETABLE'[Date],"mmyy") = FORMAT(MIN('DATETABLE'[Date]),"mmyy"),
        ALLSELECTED( 'DATETABLE' )
    )
VAR __MaxDateValue = 
    CALCULATE(
        [ASP],
        FORMAT('DATETABLE'[Date],"mmyy") = FORMAT(Max('DATETABLE'[Date]),"mmyy"),
        ALLSELECTED( 'DATETABLE' )
    )
RETURN
    DIVIDE( __MaxDateValue - __MinDateValue , __MinDateValue )

[Anonymous]

This worked perfectly, thank you!