Tableau row level calculations to compare previous row value and current row value

Tableau row level calculations to compare previous row value and current row value

If current row value is greater than previous row value then calculate: 
Current row value - previous row value

= IF INDEX() == 1 THEN
    ATTR([Delay Minutes])
ELSEIF    ATTR([Delay Minutes]) > LOOKUP(ATTR([Delay Minutes]), -1) THEN
    ATTR([Delay Minutes]) - LOOKUP(ATTR([Delay Minutes]), -1)
ELSE 0
END