Annotated vinyl test record.
HiFi for Pleasure/Response Records Stereo Test Record: 1979.

This picture has been illuminated using a small bright light held at the record's edge so as to reflect from the left channel wall of the recorded groove (the wall closest to the record centre). This clearly shows the increasing amplitude of the 300Hz lateral and vertical cut test tracks.

Another interesting feature revealed by this lighting is the difference in appearance of the left-channel-only and the right-channel-only tracks (first and second from the edge).
Theoretically, the left wall of the right-channel-only track should be completely smooth. Using the silent tracks between tests for comparison, it (almost) is.

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