Still another object of the invention is to provide a focus transparency which can be stored in {TAIL ~ a protector} and whose image is that of a test pattern useable in conjunction with a registration device for centering and {HEAD ~ focusing} of the overhead optical projector before beginning a presentation of visual aid transparencies 
Still another object of the invention is to provide a focus transparency which can be stored in { TAIL ~ a protector } and whose image is that of a test pattern useable in conjunction with a registration device for centering and { HEAD ~ focusing } of the overhead optical projector before beginning a presentation of visual aid transparencies
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