The oscilloscope is an alternative display driven from two sawtooth generators and the video signal. It gives a quite creditable picture when the astigmatism is misadjusted as shown to give fatter than usual lines. Its major visible shortcoming is the lack of frame-retrace blanking, which results in the diagonal line across the picture. The disk has essentially zero "retrace" time, so you can see in the retrace line part of the first line of video (there should be two lines of gray scale on each side of the picture).
Since the scope is accurately synchronized and the image is still, I was able to use a longer shutter time than for the disc, so that all the lines are visible.
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