AFAIK 'static' vs. 'dynamic' price ladder is the answer, see
www.elitetrader.com/vb/showthread.php?threadid=44736
www.elitetrader.com/vb/showthread.php?threadid=53954
www.elitetrader.com/vb/showthread.php?threadid=55104
www.elitetrader.com/vb/showthread.php?threadid=56833