| 摘要 |
A picture display device comprising a cathode ray tube of the index type has two patterns of index elements which are electrically separated and each generate separate signals. A first pattern, which is preferably positioned at the blind edge of the display screen, can detect large-scale and, hence, low-frequency disturbances. A second pattern, which preferably extends in the visible part of the display screen, can detect high-frequency disturbances.
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