Lessons will be scheduled in single periods unless specified otherwise. You have to allow or request double periods in the field "Double pers." of each lesson concerned. Use this field to specify the minimum and maximum number of double periods:
The entry "1-1" indicates that precisely one double period is being requested for the specified lesson.

"0-1" means that a 2-period lesson can be scheduled in a double period, but it is not an absolute requirement (minimum 0, maximum 1 double period).

An entry of "1-2" means that a 4-period lesson can also be scheduled in on double period or two double periods. The timetable algorithm should decide which variant is best suited from the overall timetable perspective.

Tip: Double-period condition
If it is possible to allow variability in scheduling double periods (e.g. with the 0-1 or 1-2 options) please allow the algorithm to work with these freedoms since this will lead to a significantly better overall result.