In this case, the 8 bit DAC doesn't imply a fixed 256x256 "grid resolution", but the "velocity" (which I am not sure is a completely valid name for it either).

In this case, the 8 bit DAC doesn't imply a fixed 256x256 "grid resolution", but the "velocity" (which I am not sure is a completely valid name for it either). The beam moves relative to its last position, and the overall magnitude of its movement depends on a different register value.