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You Can Still Use Your Calipers, If You Really Want To.
 

I constantly hear that where profile of a surface is used, you have to use a coordinate measuring machine or some other sort of high-tech inspection equipment. The assumption is that if the part had been toleranced with the old plus/minus approach, rather than geometric tolerancing, the part would be much easier to inspect with simple equipment such as calipers. Of course this is nonsense. A caliper measurement is a one-dimensional measurement of a three-dimensional feature whether it is toleranced with GD&T or not. Calipers may be used on this part, for instance, to do a quick check of features with a profile tolerance applied. Since the profile of a surface tolerance is relative to the datum reference frame established by A, B and C, an accurate, 3-D inspection of these features would require establishing the datum reference frame and measuring from the datums. Here are a couple of quick caliper type measurements that could be made..
 

Imagine trying to inspect the R8 dimension if it had been toleranced without GD&T as is shown here. Try to determine if the center of the 4X R80.1 are on the 360.1 and at the implied 90030'. By the way, how centered does the 36 have to be on the 28. There are many ways to "interpret" this drawing. However, the drawing with GD&T has "one clear meaning." Bottom line, if you want to do an inadequate job of inspecting a part using calipers-go ahead, regardless of how the part is toleranced.

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