per a 2006 Bloomberg video, Tom Demark recommended using TD Aggressive Sequential and TD Aggressive Combo in order to “get in” more trades. You may not get in (or sell out) right at the bottom (or top) but it is still a low-risk entry or exit.
Normally the TD Countdown compares the Close to the Low or High (for Buy or Sell) 2 bars prior.
For TD Aggressive, compare the Low to Low, or High to High 2 bars prior. (ie. replace Close with Low or High)