Gets or sets the level (alpha) parameter of Holt-Winters specifying how to smooth the level component. Must be within the half-open unit interval (0, 1]. A small value means that older values in x are weighted more heavily. Values near 1.0 mean that the latest value has more weight. NULL means that the HoltWinters function should find the optimal value of alpha.

public Nullable<double> Level { get; set; }