Bollinger band trend as a function
BBTrendF(expr, len1, len2, mult)
expr - data series formula
len1 - first lookback period
len2 - second lookback period
mult - number of standard deviations
The BBTREND indicator always uses the series of closing prices for its calculations.
This function makes it possible to calculate the Bollinger band trend of any series of values.
This function supports ultra-fast one-pass calculation when used in the Data Section with a non-variable count.