In this step you define weighting groups for use in your plan forecasts.
Using a weighting group only makes sense if you are using the forecast strategy "Weighted moving average". This lets you weight the past periods you use for the forecast individually to calculated the forecasted values.
The numbers in the weighting group have the following meanings:
1 - current period minus one (last period)
2 - current period minus two (second-last period)
3 - current period minus three (period before the second-last period) and so on.
Define your weighting groups.