Select the Sigmas link in the left list.
To specify an Additive type of Sigma, enter a value for the variance.
To specify a Proportional type of Sigma, enter a value for the variance.
To specify a Combined type of Sigma, enter variance values in the associated Additive and Proportional fields.
Note: The values must be a non-negative real number. A value of 0 excludes that Sigma type.