Bollinger Bands

BollingerBandsTop(Vector, Periods, Standard Deviations, MA Type) or
BBT(Vector, Periods, Standard Deviations, MA Type)

BollingerBandsMiddle(Vector, Periods, Standard Deviations, MA Type) or
BBM(Vector, Periods, Standard Deviations, MA Type)

BollingerBandsBottom(Vector, Periods, Standard Deviations, MA Type) or
BBB(Vector, Periods, Standard Deviations, MA Type)

Overview
Bollinger bands rely on standard deviations in order to adjust to changing market conditions. When a stock becomes volatile the bands widen (move further away from the average). Conversely, when the market becomes less volatile the bands contract (move closer to the average). Tightening of the bands is often used as an early indication that the stock’s volatility is about to increase.

Interpretation
Bollinger Bands (as with most bands) can be imposed over an actual price or another indicator. When prices rise above the upper band or fall below the lower band, a change in direction may occur when the price penetrates the band after a small reversal from the opposite direction.

Recommended Parameters
Vector: CLOSE
Periods: 20
Standard Deviations: 2
MA Type: EXPONENTIAL

Example
set BUY = CLOSE > BBT(CLOSE, 20, 2, EXPONENTIAL)
Evaluates to buy when the close is greater than a 20-day Bollinger Band Top calculated by 2 standard deviations, using an exponential moving average.