Average Directional Index (ADX) indicator is commonly used to measure the strength of a trend in the market. It is calculated by using the difference between up- and down- days, divided by the number of up-days. It is plotted on a graph as a histogram, with bars to represent the frequency of occurrences.The ADX can be used in many different ways, but it is most commonly used to predict when there will be an upcoming change in trend direction. The ADX typically rises as trends become more powerful and falls as trends become weaker. When it rises above 25 or falls below -25, this may signal that a change in trend direction is likely to occur soon.