| 摘要 |
A piece of tube (6) is vertically supported centrally in the lid (4) of a housing (1). This piece of tube (6) can be rotated with its ends so that it can always be held in the perpendicular. For this purpose, two spirit level bubbles (8) are arranged at right angle to one another on or at a plate (7) attached to the lower end of the piece of tube (6). The fluid in these bubbles conducts the electric current and has electric contact points for operating in each case one electric motor (10, 11) per bubble. The electric motors are provided with eccentric shafts which come into contact with the circumferential surface of the piece of tube (6). If the piece of tube (6) deviates from the particular, the current of batteries ensures that the piece of tube (6) is returned to the perpendicular via the shafts. The laser light source is located in a lower part of the piece of tube (6). A further piece of tube is inserted into the upper end of the piece of tube (6), which carries a head (16) with window (17) and can be placed into rotation by a third electric motor (18). The laser beam arrives vertically in the head (16), is there deflected into the horizontal and emerges from the window (17) as a horizontal laser beam. <IMAGE>
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