Select the Sigmas link in the left list.
Enter the value of variance to use for Sigma in an Additive residual error model.
Enter the value of variance to use for Sigma in a Proportional residual error model.
Below the Combined proportional and additive residual error model heading, enter the values of variance to use for Sigma in the additive part and the proportional part in the corresponding fields.
Note: The values must be a non-negative real number. A value of 0 excludes that Sigma type.