In the seasonal branches of activity mentioned in Article L. 3132-7, a company or establishment agreement concluded in application of Article L. 1244-2 or, failing that, a branch agreement or a professional or interprofessional agreement may, under conditions determined by decree, derogate from the provisions of this section relating to the determination of reference periods for the calculation of overtime and compensatory rest. The convention or agreement also organises contradictory procedures for counting working hours and periods.