What is the role of the Quality control grades in OB classification?

Quality Control of OBs executed in Service Mode will be based on the specified constraints in the OB for airmass, atmospheric transparency, image quality/seeing, moon constraints, twilight constraint, as well as Strehl ratio for Adaptive Optics mode observations (as requested). If all constraints are fulfilled the OB will get assigned Quality Control grade "A", while the "B" quality control is assigned if some constraint is up to 10% violated. The observations with quality control grades A or B are completed and the corresponding OBs will have status C(completed) in the database. Observations with quality control grade "C" (out of constraints) will have status M(ust be repeated) in the database and they will be re-scheduled and may be repeated. In exceptional cases an OB may get status C(ompleted) with quality grade "D", meaning that it was executed out of constraints but will not be repeated.