ADX

ADX is an oscillator that fluctuates between 0 and 100. Even though the scale is from 0 to 100, readings above 60 are relatively rare. Low readings, below 20, indicate a weak trend and high readings, above 40, indicate a strong trend. The indicator does not grade the trend as bullish or bearish, but merely assesses the strength of the current trend. A reading above 40 can indicate a strong downtrend as well as a strong uptrend.

ADX can also be used to identify potential changes in a market from trending to non-trending. When ADX begins to strengthen from below 20 and/or moves above 20, it is a sign that the trading range is ending and a trend could be developing.
When ADX begins to weaken from above 40 and/or moves below 40, it is a sign that the current trend is losing strength and a trading range could develop.

When used with DMI - the ADX is bullish when it is over both +DMI & -DMI.