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Control of Datum Features
Another Control of Datum Features Tip  

   Make Certain You Have Controlled Your Datum Features!

In most cases, datums are established from the extremities or high points of datum features. Measurements are then made from the true geometric counterpart of the datum feature. Consequently, datum features often do not get checked unless there is a tolerance that affects the datum feature. On the first drawing, the form (flatness) of datum feature A is controlled by the size toleranc of 0.1mm. It would not be necessary to add a flatness control unless the design requirement for flatness was tighter than 0.2mm.

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