You enter a new limit date of forecast period while clicking on the Add button. The monthly calendar is posted. You select there a date which is deferred in the forecasts period list.
New dates can be easily created by using the buttons, Day, Week or Month.
To remove a period, select a date in the list then click on the Delete button.
One validates the modification of the forecasts periods by OK.
If the period list is modified, the existing forecasts are readjusted to the next forecast of the list.