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Geometric requirements

Separate the datum feature, simulator and datum

The physical feature has imperfections. The datum is an ideal reference established from the specified features and rules; a simulator helps establish that reference in inspection.

Sources and scope ↓

Three things to identify

Record the real datum feature, the fixture or measurement simulation used to associate with it, and the resulting ideal reference. These are related but not identical.

Follow the specified relationship

Set up the primary and subsequent references as the drawing requires. An arbitrary best-fit alignment may answer a different question from the specified datum reference frame.

Source context

The linked manufacturer tutorial illustrates the concepts using older ISO/ASME editions. It is not a substitute for the datum-establishment rules of the user’s current drawing.

Continue your task

Read a geometric tolerance as a complete requirement →Circular runout versus total runout →True position is the target, not the tolerance zone →

All tolerance and surface references →

Sources and review scope

Reviewed 23 October 2026. Arithmetic examples are labelled separately from source-table facts and standard scope.

KEYENCE — Datum features

Conceptual distinction between datum feature, simulator and datum; its examples cite ISO 5459:2011 / ASME Y14.5-2009.

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