| 摘要 |
The device comprises a disc on which there is an arrow (9) and first and second colour markings (10,11) on either side of the arrow. The disc is rotatably connected to a stationary unit via a rotating union (3,4) so that it can rotate in its plane in relation to the stationary unit. The union is sprung in a direction normally to the plane of the disc with its spring force directed so that the disc is pushed against the stationary unit. Both disc and unit have guides (7,8) for engagement with each other on opposite sides to provide a predetermined angle position of the one to the other. The disc has a grip (6) by means of which it can be drawn out of engagement with the stationary unit so that it may be turned to another angle position for engagement with the unit. |
