This screen finds a Bollinger Band squeeze: the bands have narrowed to their tightest width in a recent period. Bollinger Bands(20,2), created by John Bollinger, plot a 20-day simple moving average as the middle band and upper and lower bands two standard deviations away, so the bands widen when volatility rises and narrow when it falls. A squeeze shows that volatility has contracted to a low level, and since quiet periods tend to be followed by large moves, traders watch for a breakout from the bands.
