Which of the following statements accurately defines a datum symbol on a GD&T drawing?

• A. A circled letter marking the datum.
• B. A plain letter next to a dimension.
• C. A surface roughness symbol.
• D. A leader line.

Answer: (A)

A datum symbol is shown on a GD&T drawing as a circled letter. That circled letter marks the datum feature—the reference surface, axis, or point used to establish the measurement frame for tolerances. The circle makes it clear this is a datum marker, not just a label or other symbol. The other choices don’t fit because a plain letter next to a dimension isn’t the datum indicator, a surface roughness symbol represents another type of tolerance, and a leader line is just a drawing connector, not the datum designation. In practice, datums are defined by these circled letters and then used in the datum reference frame to control how features are measured and oriented.