Granite square feet according to the national machinery industry standard: JB/T10027-99 manufacturing. For perpendicularity, parallelism testing, and can serve as an absolute measurement of the benchmark 90 °. 
 Size (mm) collar the two measurements perpendicular 
 Measuring surface straightness 
 Relative measurement of surface parallelism 

 Accuracy rating um 

 00 
 0 
 00 
 0 
 00 
 0 

 160 × 160 
 2 
 4 
 0.8 
 1.7 
 2 
 4 

 200 × 200 
 2 
 4 
 0.9 
 1.8 
 2 
 4 

 250 × 250 
 2.2 
 4.5 
 A 
 2 
 2.2 
 4.5 

 315 × 315 
 2.6 
 5.2 
 1.1 
 2.3 
 2.6 
 5.5 

 400 × 400 
 3 
 6 
 1.3 
 2.6 
 3 
 6 

 500 × 500 
 3.5 
 7 
 1.5 
 3 
 3.5 
 7 


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