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