Theory :
Originally volatility quality was invented by Thomas Stridsman, and he uses it in combination of two averages (original was published, with some more explanation, here : Volatility quality Stridsman)
This version :
It is not using averages for trend estimation, but is using the slope of the Volatility quality. In order to lessen the number of signals (which can be enormous if the VQ is not filtered), some versions similar to this are using pips filters. This version is using % of ATR (Average True Range) instead. The reason for that is that :
Additionally, this version is made to oscillate around zero line (which makes the potential levels, which are even in the original Stridsman's version doubtful, unnecessary)
Usage :
You can use the color change as signals when using this indicator

Volatility quality
Volatility quality with ATR filter
Nonlinear Kalman filter deviation
Nonlinear Kalman filter deviation
Stripped T3 levels
Stripped T3 levels (T3 levels that can display the 3 phases of T3 calculation)
MinMax indicator
MinMax indicator