Average Constant line creation is not working

I have created a line graph which is filtered using a date range picker. . And the chart is getting dynamially changed when we are back dating the values. Aditionally I needed an average value for Last year for the below chart. That means the dark blue color line.  As you can see, the average is a constant line.  

Avg sales = CALCULATE( IFERROR( 
    [LY Sales]/[Measurecal],
    BLANK()
    ), ALL('Date'[Date]))

LY Sales = CALCULATE([Sales], SAMEPERIODLASTYEAR('Date'[Date]))

Measurecal = 
VAR StartDate =  DATE ( YEAR(MIN('Date'[Date])),MONTH(MIN('Date'[Date])), DAY(MIN('Date'[Date])) )
VAR EndDate =    DATE ( YEAR(MAX('Date'[Date])),MONTH(MAX('Date'[Date])), DAY(MAX('Date'[Date])) )
return DATEDIFF(StartDate,EndDate,DAY)

Below Is the chart that gives incorrect figure. 
.  when we select the date period Jan 7 2021 to Nov 18 2021, the avrage should be 1172 not 989.13. And the average value constant line should  changed dynamically when we change the date range.  Can you pls help? I have attached the workbook 

https://drive.google.com/file/d/12cItFy_wdfWHsbg0qLry93pFBd88LujY/view?usp=sharing

thanking you in advance