Adding a semester is only premitted if a semester has ended, or there is no active semester. To add a semester, make sure that the "''Add''" radio button is selected. You may then select a semester ID from the drop down lists, which is unique and does not exist already. You may then select a start date for the semester, the start date must be after the end date of the previous semester (if any), but not later the the selected end date for the newly added semester. You may also select an end date for the semester, which must be later than the start date. Neither dates may be left blank. Once all fields have been validated, you may click the "''Add Semester''" button. For reference, see ''Figure 3.910''