Abstract: The method serves for the interferometric measurement of non-rotationally symmetric wavefront errors on a specimen . The specimen is brought into a number of rotational positions, at least one measurement result being determined in each of the rotational positions and a mathematical evaluation of all measurement results is performed. The measurement results (M1 . . . Mm; N1 . . . Nn) of each of the measurement series (M, N) are determined respectively in mutually equidistant rotational positions of the specimen . The measurement results (M1 . . . Mm, N1 . . . Nn) of each of the at least two measurement series (M, N) are evaluated independently of one another for non-rotationally symmetric wavefront errors (<W>m, <W>n) on the specimen, and a difference is computationally rotated m or n times and the results averaged out. At least one of the wavefront errors (<W>m, <W>n) is corrected with the result (<<W>m-<W>n>m or <<W>m-<W>n>n) averaged in this way.

Abstract: A plastic mounting plate closes a electrical box which delivers wires to an alarm unit or emergency light or the like. The alarm unit is mounted to the mounting plate by a snap connection and a tab-in-slot connection, without requiring the use of a tool. The mounting plate is connected to the electrical box by screws which engage threaded holes provided by the electrical box. The mounting plate can be mounted to either a single-wide electrical box or a double-wide (4×4) electrical box and provides corresponding holes for connection to either box. An alternate mounting plate for a single-wide electrical box is also provided.

Abstract: A venetian blind of the vertical louver type includes an elongated guide track and a plurality of louver carriers supported by the guide track for traverse between open blind and closed blind conditions. Each of the louver carriers supports a louver in generally vertical orientation for traverse with the carrier and for rotation about its longitudinal axis between open and closed louver positions. A louver operating mechanism is supported on one end of the guide track and is operative to rotate the louvers to open louver positions prior to traverse along the guide track from a closed blind condition to an open blind condition. A rotation rod extends longitudinally of the guide track in cooperative relation with the louver carriers and supports a rotation pulley actuated by a beaded chain to rotate the rotation rod and effect rotation of the louvers.