Abstract: A testing and calibrating device for optical eye length measurement devices comprising two plano-convex lenses which are arranged in the illumination beam path so as to be oppositely oriented. A neutral filter with a defined transmission is located between these two plano-convex lenses.

Abstract: A workpiece, designed as a printed circuit board for example, can be moved by means of a transport device under a laser unit in such a way that a region to be machined of the workpiece passes into the deflecting region of the laser beam. The workpiece is set between clamping jaws to a vertical position in which the laser beam is focused exactly on that surface of the workpiece which is to be machined. As a result, the machining accuracy can be considerably increased.

Abstract: A convergence tube for stereomicroscopes in which both observation beam paths are inclined relative to one another at an angle of convergence &agr; and image inversion elements are provided in both observation beam paths. Four planar reflectors R1 to R4 are provided in each of the two beam paths and are arranged relative to one another in such a way that the axis beams incident on and emergent from the reflectors R1, R2 lie in a common plane E1,2, the axis beams incident on and emergent from the reflector R3 describe a plane E3 that forms an angle &bgr;=90°+&agr;/4 with the plane E1,2, and the axis beams incident on and emergent from the reflector R4 describe a plane E4 that forms an angle &bgr;2=&agr;/2 with plane E3.

Abstract: Described are methods which preserve the order of the data frames within a data stream if the data stream is switched from one link to another. The first method achieves the order preservation by numbered switch frames that have to be exchanged between the nodes before the link switching is actually performed. In the second method, the switching is only prepared by exchanging special frames which indicate "clean" links. Actual switching takes place by just using an already prepared, i.e., "clean" link.

Abstract: In the exemplary embodiment, two machines are arranged in a common cabinet-like housing insulated toward the exterior from sound conducted through solids and airborne sound. For the purpose of fresh air supply to the machines, there are provided common fresh air channels connected via an inlet port with the exterior air. In order to discharge the exhaust air, separately arranged exhaust air chambers and/or exhaust air channels are provided which discharge into the open air via a common outlet port, disposed at a location remote from the inlet port. The fresh air channels and the exhaust air channels are so designed and arranged that the air is deflected many times during its flow through the housing. The installation particularly serves the purpose of housing dental vacuum generating and compressed air generating electric machines.