The Extreme Point Rule
The directional movement indicator is a powerful tool for spotting shifts in market momentum. A buy signal is given when the positive directional indicator ( DI) crosses above the negative directional indicator (-DI), and conversely, when negative directional indicator crosses above the positive directional indicator a sell signal is generated. When the market is trendless the DI lines crisscross back and forth, which can generate false signals.
Solely following the DI and -DI cross signals by themselves can lead to whipsaws and overtrading. Steven Achelis offers a solution to this problem using the ?extreme point rule? in his marvelous book, Technical Analysis From A To Z. Achelis points to the creator of the directional movement system J. Welles Wilder, and his simple trading rule, to help prevent whipsaws and reduce the number of signals that a trader acts upon.
The extreme point rule requires a trader to mark the extreme price point the day in which the DI and -DI cross. According to Achelis, the extreme point is highest of point of a session when DI crosses above -DI and is the lowest point of the session when -DI crosses above DI. Buy or sell signals are triggered when prices move beyond the extreme point.
This explanation of the Directional Movement Indicator sell signal is from Ron Walkers chart list http://thechartpatterntrader.com/
