The fully variable three-knife trimmer, SigmaTrimmer, works using an innovative cutting principle. It consists of three independent cutting elements and allows the changeover of size and thickness without empty cycles while the machine is running. Each books guided by a clamp to the individual cutting stations. While this is happening, the books are constantly held and always retain their alignment. First the foot and then the front and finally the head cut are carried out, according to the circle principle. The distance of each clamp to the knife is individually controlled in each cutting position and thus allows full variability of the final size of the book. The format data is transferred from the line control to the SigmaTrimmer with the right cycle timing. The pressing along the entire length of the trim, and the swing cut technology against a cutting stick, guarantee that the end product is of the highest quality.