ClearEdge VM wideband velocity modulation improves the definition at
picture edges, creating sharper images by slowing the CRT (cathode-ray
tube) beam's horizontal scanning during demanding work--say, when
rendering transitions from light to dark parts of an image--and
speeding it up when scanning easily rendered sections, like broad dark
areas.

From a Sony WEGA blurb....

So it seems there are some possiblities for other than standard
constant velocities in raster scanning.

Doug Goncz
Replikon Research
Falls Church, VA 22044-0394