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Counting the Profile Tolerance Twice.
 
Here is another example to help explain why the profile tolerance is on the surface, not on the dimension. The length of this part is dimensioned two different ways - with a 90mm overall or a 2X 45. Which one will allow the part to vary more? The answer is at the bottom of the figure.
 

Answer: There is no difference. The Max and Min values are the same no matter how the part is dimensioned. The tolerance is on the surfaces not the dimensions. The width can vary from 90.4 to 89.6 because each surface has a total tolerance of 0.4 based on the profile of a surface tolerance.

 
   

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