There are two sets of deflection magnets: the (slow) main field deflector and the (fast) trapezium deflector. The origin of each shape is first set with the main deflector, and then that shape is filled in using the fast trapezium deflector. Each deflector is driven by a separate DAC: the main field has a 20 bit DAC and the trapezium deflector has a 14 bit DAC. (You don’t know what a DAC is? Look it up.)