At least one lesson per week has to be in certain classroom

Let' say you have more classrooms for your Physical Education lessons (few Gyms with different sizes -"big and small" , Playground for outdoor activities, Fitness gym with specific equipment in the school basement).
Generally you want the kids to be always in the Big Gym classroom, but you know this is not possible. Some of the PE lessons need to be also in Small Gym, or outside on Playground)

To make sure, that each kid is at least once per week in the best classroom you can use following:

1. At first make sure that you have defined all the Gym rooms as available to all PE lessons. Then the software can choose any of them during the generation. See these articles:
Asignar lecciones a aulas
How can I specify default (usual) classrooms for certain subject?

2. Then add the advanced card relationship nb. 51 "Min periods per week in selected classrooms".
In Advanced dialog select:
- min = 1 - So at least one PE lesson per week shall be in BigGym
- Apply to groups in selected classes - If you divide your PE lessons to groups Girls/Boys, this would guarantee the BigGym at least once for each group. If you however just select "Apply to selected classes" the generator will only check if there is one PE lesson per class, which will mean that only boys will be in BigGym.
- the classroom - in our case it will be the "Big Gym"
- the subject - it will be "Physical Education"