Buy alerts are signalled when the +DI lines crosses the –DI line from below and sell signals are given when the –DI crosses the +DI line from below. The strength of the signals provided by the intersections of +DI and –DI can be obtained from the ADX line, this is why the two indicators should be used in unison. Higher readings of the ADX (in general above 25) confirm a firm trend giving confidence to the +DI/-DI crossovers, readings below 20 imply that the trend is weak and that users may wish to ignore the +DI/-DI crossing.
Users may wish to adopt Wilders "rule of points of extremum" to help reduce the potential for false trades. This rule specifies that where +DI crosses the -DI from below a trader will not initiate the buy trade until the upper extreme of the period in question is breached (maximum of candle), and where the –DI crosses the +DI from below traders will not initiate the sell trade until the lower extreme is breached (minimum of candle)