The teacher makes the app (via Button) generate an event-nr.
He tells this event-nr to the pupils. They enter the event-nr into their feedbackSender-app.
Whenever now the teachr wants a feedback, he pushes
start feedback "NOW! (for about 25 sec)".
Each pupil now can give one feedback ( A red, B yellow, C green).
After 25 seconds the teacher can see the accumulated Feedbacks as numbers and as diagram.