Check the straightness of the working surface of the cast iron ruler

Use equal height blocks to support the Type I and Type II straightedge at the standard support marks 2L/9 from both ends of the straightedge, and select the appropriate bridge deck according to the length of the working surface of the straightedge (usually 8-10 steps, with a span between 50 and 500mm); Then place the bridge deck at one end of the ruler and fix the reflector or level on the bridge deck; The bridge deck is gradually moved from one end of the straightedge to the other end according to the span, with a division value of 1 for each span moved; Read the reading at that position on an autocollimator (or 0.005mm/m) or an electronic level with a division of 0.001mm/m (a combination level with a division of 0.01mm/m can be used for a first level ruler with a working face length greater than 500mm, and a frame level with a division of 0.02mm/m can be used for a second level ruler); The difference is the straightness error of the straightedge working surface. The straightness error of any 200mm on the working surface can be determined by selecting 50mm or 100mm bridge slabs and inspecting them within any 200mm using the above method. For flat rulers with a working face width greater than 60mm, they should be inspected according to the flatness requirements, and the flatness tolerance value should not exceed the straightness tolerance value specified in Table 2.