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There are two kinds of straightness tolerance – (1) Straightness of a derived median line [Y14.5-2009 Fig 5-2 and Y14.5-2018 Para 8.4.1.3] and (2) surface straightness [Y14.5-2009 Para 5.4.1.1 and Y14.5-2018 Para 8.4.1.2]. The type of straightness is determined by the placement of the feature control frame.
When the feature control frame is …