Baseline (datum) dimensioning — reference feature In baseline dimensioning, all dimensions originate from a single common geometric reference. What is this reference called?

Introduction / Context:
Dimensioning schemes affect manufacturability, inspection, and tolerance accumulation. Baseline (datum) dimensioning reduces stack-up errors by measuring all features from a common reference rather than chaining dimensions from feature to feature.

Given Data / Assumptions:

• The method used is baseline (also called datum) dimensioning.
• One primary reference feature is selected to control measurement origin.
• Standards often designate datum features with specific symbols.

Concept / Approach:
A datum is a theoretically exact reference—plane, axis, or point—from which measurements are taken. In drawings, selecting an appropriate datum (such as a machined face or a bore axis) provides repeatable fixturing and consistent inspection references, minimizing tolerance accumulation compared to chain dimensioning.

Step-by-Step Solution:

Verification / Alternative check:
ASME Y14.5 defines datum features and datum reference frames; baseline dimensions are measured from a designated datum to each feature requiring location control.

Why Other Options Are Wrong:

• Edge/corner: may serve as a physical datum but are not the general term.
• Point of reference: informal phrasing; the standardized term is “datum.”
• Anchor notch: not a recognized standards term.

Common Pitfalls:

• Selecting a poor datum (e.g., rough, nonfunctional surface) leads to manufacturing and inspection inconsistency.

Final Answer:
datum