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Bollinger Bands Trading System

The Bollinger Bands Trading System is a volatility trading system which requires the calculation of volatility (in terms of the standard deviation). The volatility band gets plotted above and below the current market price of the stock.

The upper band (BBT) is the +2 standard deviation above the prices and the lower band (BBB) is the -2 standard deviation.

A buy is suggested when the current market price touches BBT and a sell is suggested when the current market price touches BBB.

Buy script

SET Bottom = BBB(CLOSE, 20, 2, EXPONENTIAL)
SET Top = BBT(CLOSE, 20, 2, EXPONENTIAL)
((REF(CLOSE, 1) < REF(Bottom, 1)) AND
CLOSE > Bottom

Sell script

SET Bottom = BBB(CLOSE, 20, 2, EXPONENTIAL)
SET Top = BBT(CLOSE, 20, 2, EXPONENTIAL)
((REF(CLOSE, 1) > REF(Top, 1)) AND
CLOSE < Top

Additional notes

BBB and BBT are predefined functions in the Tradescript.
20 refers to the 20 day period and 2 refers to the number of deviations. These are the standard parameters of a Bollinger band system.