A reference dimension is used only for information purposes. The indication "REF" should be noted immediately under or beside the dimension. Normally it is either a duplication of a dimension or the accumulated value of other dimensions. Reference dimensions are typically located within parentheses. Reference dimensions do not have tolerances and should not be used to manufacture or inspect parts. The purpose of reference dimensions is to provide additional information. Some prints may not show reference dimensions within parentheses and instead show "REF" or "REFERENCE" after the dimension (Figure 4.10).
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