用自准直仪测量机床或仪器导轨的直线度，目准直仪的放置应稳固可靠。其放置方法有两种：一是安置在导轨之外专用支架或台桌上，一是安置在导轨工作面上。由于从仪器发出的平行光为测量基准，所以若安置不当，将产生较大的测量误差。前一种方法如采用不可调的专用支架难以使桥 Use self-collimator to measure the straightness of the machine tool or instrument guide rail. The placement of the sight collimator should be stable and reliable. There are two ways to place it: First, placed in a special rack or table outside the guide rail, one placed in the guide rail face. Due to the parallel light emitted from the instrument as a measurement basis, if placed improperly, will have a larger measurement error. The former method, such as the use of non-adjustable special bracket difficult to make the bridge