ASME Y14.5 : Dimensioning and Tolerancing
Dimensional information, usually without a tolerance, that is used for reference purposes only. A reference dimension is a repeat of a dimension or is derived from other values shown on the drawing or on related drawings. It is considered auxiliary information and does not govern production or inspection operations. Where a basic dimension is repeated on a drawing, it is not identified as reference.
See Also:
Tolerance, Dimension, Drawing, Basic Dimension