in a balancing system and a method for balancing a drum of a printing plate exposer , at least one mass element is provided which can be moved substantially in the circumferential direction of the drum in order to reduce an imbalance of the drum . previous devices and methods either needed the expertise and the knowledge of a user or external actuators which had to be driven by corresponding devices , for example computers , in order to compensate for an imbalance by moving the mass elements . the balancing system is simple and automatic balancing of the drum is achieved by a mass element being coupled to a positioning element and by its position being adjusted automatically on the basis of the circumferential extent of the printing form .