This function is meant to handle recuring events that occurs at different dates/period from one year to the next like Easter, Thanksgiving, Chinese New Year... Such holidays/events can have a huge effect on the sales of the part and since it the holiday/event occur in different periods from one year to the next it can not be handled with seasonal profiles. In fact such holidays will mess up the parts seasonal pattern an make the seasonal algorithms to not work properly.
The recuring event function is buildt up like this, there are one recuring event template which is a collection of recuring event details, a recuring event template is what you connect to the part with selecting the wanted recuring event template for the part, see Detail view (recuring event). A recuring event detail is how you define one recuring event it has a name and the number of days that are affected by this recuring event, and it also includes which days in the past and in the future that are affected by the recuring event. This allows the parts forecast to be affected by many recuring events per year.
The recuring event approach in Demand Planning is to find a normal daily sales, this sale will represent what the sales qty for a day within the recuring event would be it the recuring event did not occur. This normal day sales is computed by doing a exponential smoothing (EWMA) of the daily sales for each daily sales that is not part of a recuring event. The alpha used is set in the Demand Plan Server, Advance Server Settings. ForecastModels\Holiday\AlphaDayQty see Advance Server Settings. Recommended values for this day alpha is between 0,02 to 0,08 default is 0.045. Note there is a pitfall with the recuring event functionality. If a recuring event occur close to a high selling period, but the recuring event itself is not in this high selling period, the recuring event indexes computed for this holiday will be to low so the recuring event effect will in turn be on the low side.
During the recuring event period the recuring event indexes are computed for each day of the recuring event. A recuring event index is computed like this recuring event index = Actual Sold Qty / normal day qty. This index is used to increase the forecasted daily qty in the future recuring event period. The adjusted demand in the recuring event period is set to be equal to the normal day qty (computed by the AlphaDayQty EWMA algorithm described above), the Demand is as always set to the actual qty sold. The recuring event indexes is also smoothed out from one recuring event occurrence to the next, this is also done by a exponential smoothing (EWMA) of each daily index. The alpha smoothing constant is set in the Advance Server Setttings entry ForecastModels\Holiday\AlphaHolidayIndex, default value is 0,6 is the default setting for this constant, so the last recuring event occurrence will get a high weight when computing the future recuring event index.
As a summary the movable recuring event function works like this, we remove the recuring event effect from the adjusted demand so that it will not have an effect on computing seasonal profiles and the future forecast. Then we add the forecasted recuring event effect to the future system forecast, with the computed recuring event index day by day in the future forecast.
It can be clever to only connect a recuring event template to parts that you know are effected by the recuring event, and keep unaffected parts outside the recuring event calculation, since these will effect the global recuring event index for this recuring event, and the global recuring event index is used to compute the recuring event effect on parts that do not have history, and it can also be used on parts whit history trough the recuring event mix factor. It can also be smart to look at the days before and after a recuring event and see if these also are affected by the recuring event and maybe consider to add these to the recuring event period as well.