| 摘要 |
The system comprises a horizontal visual indicator (1) located on top of and parallel to the net (3). This defines with the net a sighting window by defining a guide line for the player. The visual indicator consists of a cord, an elastic cable or a luminous ray. It is fixed by arms (6,6') at a distance of about 80 cm above the upper end of the net. The arms are terminated in their upper part by a right-angle or by an elbowed part. The indicator line is advanced by about 10 cm from a side of the plane of the net. The arms are connected to the posts by a runner (11).
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