very useful indicator to make reading the bb easily , if the indicator increased means volatility increase and the price tends to move away from the BB moving average (center line ) , if the indicator decreased means the volatility decreased and the price tend to pounce back to the moving average . ( in any direction up or down )
if the indicator decrease at a candle touching the BB moving average and pounce back or crossed it no trade to be done and hold to confirm the movement direction
best used with bb or moving average of the same value .