What is the role of a datum target on curved surfaces in GD&T?

What is the role of a datum target on curved surfaces in GD&T?

• A. It declares material type
• B. It measures roughness
• C. It indicates surface color
• D. It defines the datum location for measurement on curved surface

Answer: (D)

Datum targets on curved surfaces establish where the datum reference frame is located for measurement. Because a curved surface can’t define a datum with a single plane, the target marks a precise spot on the surface that the gauge or CMM uses to locate the datum origin and its orientation. This provides a repeatable, measurable reference on the curved surface so other features can be measured consistently relative to that datum. They are not about material type, roughness, or color.

Datum targets on curved surfaces establish where the datum reference frame is located for measurement. Because a curved surface can’t define a datum with a single plane, the target marks a precise spot on the surface that the gauge or CMM uses to locate the datum origin and its orientation. This provides a repeatable, measurable reference on the curved surface so other features can be measured consistently relative to that datum. They are not about material type, roughness, or color.