Which indicator shows where on the surface the datum is established?

Which indicator shows where on the surface the datum is established?

• A. A datum target shows where on the surface the datum is established.
• B. A datum symbol marks where the datum is established on the surface.
• C. A box around a dimension indicates a datum target.
• D. A basic dimension marks where the datum is established.

Answer: (A)

In GD&T, the exact spot or region on a surface used to establish a datum is shown with a datum target. The target sits on the surface and is connected by a leader line to the precise area used to define the datum, which is especially important for curved or irregular surfaces where a single feature can’t define the datum location. The datum symbol identifies which feature is the datum, but it doesn’t specify where on the surface the datum is established. A box around a dimension indicates a basic dimension, not the location marker for the datum, and a basic dimension itself defines a theoretically exact size or location rather than marking where a datum is established.

In GD&T, the exact spot or region on a surface used to establish a datum is shown with a datum target. The target sits on the surface and is connected by a leader line to the precise area used to define the datum, which is especially important for curved or irregular surfaces where a single feature can’t define the datum location. The datum symbol identifies which feature is the datum, but it doesn’t specify where on the surface the datum is established. A box around a dimension indicates a basic dimension, not the location marker for the datum, and a basic dimension itself defines a theoretically exact size or location rather than marking where a datum is established.