{HEAD ~ Method} and apparatus for producing {TAIL ~ grey levels} on a raster scan video display device 
for producing
{ HEAD ~ Method } and apparatus for producing { TAIL ~ grey levels } on a raster scan video display device
HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH