Following a modelisation of the price variation by Fractional Brownian Motion, this indicator increases the width the Bollinger Bands in order to avoid (or minimize) false signals (of entry or exit). For a more complete explanation, please see my blog: http://fractalfinance.blogspot.com/2009/05/from-bollinger-to-fractal-bands.html
Here is what this indicator looks like for a speed of the FRASMA (https://www.mql5.com/en/code/8866) set to 30. The red indicator is the Fractal Bands, and the blue is the Bollinger Bands (with a speed set to 30 as well), below is the Fractal Graph dimension (https://www.mql5.com/en/code/8844):
The Acceleration/Deceleration Indicator (AC) measures acceleration and deceleration of the current driving force.Average Directional Movement Index (ADX)
The Average Directional Movement Index Indicator (ADX) helps to determine if there is a price trend.