The way SSA ERP determines the start date of the plan period not only depends on the setting of the Period Start field, but also on whether or not the scenario is a rolling scenario.
If you selected the Rolling Scenario check box in the Scenarios (cprpd4100m000) session, SSA ERP shifts the scenario forward in time when the value of the current date is higher than the sum of the reference date and the rolling frequency. SSA ERP then shifts the scenario forward in time by the value of the rolling frequency.
When SSA ERP rolls the scenario, it updates the dates of the plan periods and redistributes the master-plan quantities over the new plan periods.
The rolling scenario functionality applies to the entire scenario, whereas the setting of the Period Start field only applies to the way that SSA ERP determines the start date of a period with regard to the current date.
If you select a day of the week or a date of the month, SSA ERP only changes the master-plan quantities of the first plan period, as the current date advances. SSA ERP leaves the rest of the plan periods untouched.
If you select Rolling in the Period Start field, SSA ERP shifts the plan periods forward in time from the current date by the value of the Period Type field, and redistributes the master-plan quantities over the shifted plan periods.
The options that you can select are determined by the value of the Period Type field:
If you selected Day, SSA ERP defaults the Period Start field to Rolling.
If you select Week, you can select Rolling or a specific day of the week.
If you select Month, you can select Rolling or a specific day of the month.