Average Directional Movement Index Technical Indicator (ADX) assists to conclude if there is a price trend change. It was developed and described in detail by Welles Wilder in his book "New concepts in technical trading systems".
The simplest trading method based on the system of directional movement implies a comparison of two direction indicators: the 14-period +DI one and the 14-period -DI. To do this, one either puts the charts of indicators one on top of the other, or +DI is subtracted from -DI. W. Wilder recommends buying when +DI is higher than -DI and selling when +DI sinks lower than -DI.