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