This sharp divergence signals the eventual breakout after price finally reverses off of the bottom band. Watch band slope closely when bars return to test important highs or lows. The skilled eye watches constricted bands in real-time to estimate the buying or selling force required to push them out of the way. They work extremely well during the second test of an important high or low. When markets finally break out, expanding bars often shoot into the band's edge where congestion forms a flag until the BB allows further movement.
Bands constrict tightly around narrowing price in sideways markets.
Apply NR7 methodology here to anticipate an impending positive feedback event. Bollinger Bands signal early warning of trend change. Sharp price movement forces bands to expand outward. When these active markets finally turn sideways, the bands slowly tighten and roll toward price. Time passes and the BB door closes on rapid vertical movement.