| 摘要 |
An advertising board includes a plurality of groups of plates placed close by. In each group the plates are set up in a semicircle movable round the common axles. The plates standing on the straight edges of the semicircles, form together a good sight-surface of the advertising board. The number of plates in each group equals the number of different plate positionings and different sight-surfaces. The mechanism that changes position of the plates consists of a revolving and steering system.
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