The apparatus 3, including a video monitor biased to the center of gray scale so that said monitor registers zero difference between the original and copy and registers {TAIL ~ a difference signal} {HEAD ~ the level} of which is proportionate to the degree of degradation of the copy over the original 
of
The apparatus 3 , including a video monitor biased to the center of gray scale so that said monitor registers zero difference between the original and copy and registers { TAIL ~ a difference signal } { HEAD ~ the level } of which is proportionate to the degree of degradation of the copy over the original
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH