The calculation of the average directional movement (ADX)
indicator is built on the intuitive notion that a trend is a series
of price ranges extending in a consistent direction. In sidebar
Figure 1, example A, the second day’s trading range is higher
than the first day’s trading range, indicating positive directional
movement. In example B, the second day’s trading
range is below the first day’s trading range, an indication of
negative directional movement. ...