StandardErrorBands

Is a statistical indicator.
Is computed using the closing price.
Returns three time series. The first is a 3-period simple moving average of the 21-period linear regression indicator. The second and third series are bands that are two standard errors above and below the moving average.
FinancialIndicator["StandardErrorBands",n1,n2,b] uses period- linear regression, period- moving averages, and bands b standard errors from the moving average.
The first values in the time series are computed using partial periods.