Lower Bollinger Band. Bollinger Bands are moving average envelopes
that are plotted at a standard deviation level aboveand below price.
Because bands are based on standard deviation, they adjust to volatility
swings. Bollinger Bands tighten as volatility decreases, and expand
sharply as it increases. Prices normally have a tendency to bounce
within the bands envelope. But prices can exceed a band envelope for
long periods during strong trends.