To specify your own weight - Single Exponential Smoothing
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In the main Single Exponential Smoothing dialog box, choose Use under Weight to use in smoothing, and enter a value between 0 and 2, although the usual choices are between 0 and 1.

You can use a rule of thumb for choosing a weight.

·    A weight a will give smoothing that is approximately equivalent to an unweighted moving average of length (2 - a) / a.

·    Conversely, if you want a weight to give a moving average of approximate length l, specify the weight to be 2 / (l +1).