The name of the indicator might be a bit misleading. Holt's double
exponential smoothing is mostly used for forecasting, not as an average.
The forecasting method usually used with it is a sort of linear
forecasting
Like the regression forecast, the double exponential smoothing forecast is based on the assumption of a model consisting of a constant plus a linear trend.
The estimate a and b at time T are based in the observation at time T and the estimates for the previous period, T -1.
The forecast for the expected value for future periods is the constant plus a linear term that depends on the number of periods into the future.
To
make it usable in both manners though (as an average or as an "average"
with forecasting, setting the number of forecasted bars to <= 0,
turns the forecasting part off.
As usual with the forecasting parts, it is strongly advised not to use it in signaling mode. The forecasting part is a subject of change and should be used only as an estimation of trend component of the double smoothing, not as signal. Alerts in this indicator are not alerting on the change of the forecast part, but on the change of the "past" part - which is not going to change with time past
