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