Syntax

BOLLINGER(A1; period; deviation)

Arguments

A1 must be an array. The 'period' argument defines the period for the function. It must be a constant greater than or equal to 1.
The 'deviation' argument defines the number of standard deviations that the band is offset from the simple moving average of A1.
For the upper band this must be a positive value and for the lower band, a negative value.

Result

The result is an array.
The first 'period' elements of the result are marked as invalid.

Description

Bollinger bands are drawn at a given number of standard deviations from a moving average of a price. Since standard deviation is a measure of volatility, the bands are self-adjusting, widening during volatile markets and contracting during calmer periods. Bollinger Bands were created by John Bollinger. 

To draw the two Bollinger bands, you can use two line series (one for the upper band and one for the lower band) or a single Hi-Low series.

For the upper band use the following expression: "BOLLINGER(A1, 20, 2)".
For the lower band use the following expression: "BOLLINGER(A1, 20, -2)". 

Mr. Bollinger recommends using 20 periods in the moving average, and using 2 standard deviations. He has also found that moving averages of less then 10 periods do not work very well.

Related Examples

Windows Forms: Data Manipulation\Functions\Bollinger Bands
                        Series\Combo Charts\Financial Chart Example