The Forecasting Model window (for family items or for normal items, possibly associated to a given distribution center if any) is accessed by clicking on the Model button in the Sales Forecasts window. The number of future periods for which a forecast has to be generated is defined in the cell Number of periods to forecast (which in fact defines the Forecast horizon),
The forecast error criterion has to be selected in the Optimization criteria : minimize … panel,
One has to select Fct error (corresponding to the mean algebraical error), MAD (corresponding to the mean absolute error) or MSE (corresponding to the mean quadratic error).