Sales for Same Period Last year relative to a Year Slicer / Filter

[CMAC_Terry]

Need some guidance to see if I'm going about this the right way.

I'm trying to create a YoY sales Variance that calculates the variance relative to the year selected in a Year filter; this is so the consumer can click through years; see that years sales and the variance +/- to previous year. 

I've been able to calculate the selected Years' Sales relative to the slicer with this below, but the when I try to create the year before sales, same calculation but amending the: YEARSTART-1 and YEAREND-1) relative to the slicer it returns blank.

Total Job Bill = 
VAR
    YEARSTART    =  SELECTEDVALUE( FactJobEntry[Key Date.Year] , MIN( FactJourney[Key Date.Year] ) ) 
VAR 
    YEAREND      =  SELECTEDVALUE( FactJobEntry[Key Date.Year] , MAX( FactJourney[Key Date.Year] ) )
VAR
    TOTALJOBBILL =  SUM( FactJobEntry[Bill Net] ) 
RETURN
  CALCULATE( TOTALJOBBILL,
      DATESBETWEEN( FactJobEntry[Key Date],  
      DATE( YEARSTART, 1, 1 ) , DATE( YEAREND, 12, 31 ) )
      )

[CMAC_Terry · Accepted solution]

Found an answer using 

Total PY Job Bill = 
IF ( 
  ISCROSSFILTERED( DimCalendar[DimYear] ),
  CALCULATE( [Total Job Bill],
  SAMEPERIODLASTYEAR( DimCalendar[Date] )),
  BLANK())