In an additive seasonal model,we add an appropriate seasonal index to a "base" forecast.These indexes,one for each season,typically average to 0.

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In an additive seasonal model, the seasonal indices are designed to adjust the base forecast by adding or subtracting a fixed amount for each season, and they typically average to 0 to ensure that the overall level of the series is not altered.

In an Additive Seasonal Model,we Add an Appropriate Seasonal Index