... digital led digital clock 100% feedback Led digital clock with computer RS232/485 communication 1 led digital clock iterm GC406 Case dimension:710mmX160mmX40mm2 Display 4" red 6 digital led digital ... 0.5",1",1.2",1.5",1.8",2.3",3",4",5",6",8",10",12",14",16",18",20 ... to the difference between levels of blacks compared to the level of whites in the sign, Things like reflective surfaces, glare ...