For 3rd largest:

With TOPN:

PHP Code: 
MINX(
    
TOPN3SUMMARIZETable1Table1[Units] ), Table1[Units], DESC ),
    [
Units]

With RANKX:

PHP Code: 
VAR MyTable =
    
SUMMARIZE(
        
Table1,
        
Table1[Units],
        
"Rank"RANKXALLTable1 ), Table1[Units] )
    )
RETURN
    
MAXXMyTable, IF( [Rank] = 3, [Units] ) ) 
Regards