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Daven Tri-Standard Scanning Disc, 1928 (U.S.A.) The lack of a common standard of picture definition contributed to the demise of the mechanical television boom of the late 1920's and early 1930's. One solution was to make a television set that could receive a number of different standards. This Daven unit was based on a large 24" disc capable of scanning three different standards of picture definition, 24-line, 36-line and 48-line, enabling the viewer to receive more stations. The television signal was received by a short-wave radio. The operator then had to adjust the height of the neon lamp to match the correct spiral of holes, and synchronize the rotation of the scanning disc to the corresponding rotations per minute. The tiny picture would be visible in one of the three frames (marked within the black outline).