What do datums define regarding surfaces and inspection equipment?

Datums play a crucial role in Geometric Dimensioning and Tolerancing as they are reference points or surfaces from which measurements are taken. They help establish a framework for part alignment, enabling accurate and consistent inspections. The correct answer highlights that datums define the sequence of contact with the inspection equipment, which is essential in ensuring that measurements are taken from a common reference. This process helps to eliminate potential variations and inaccuracies during inspection by providing a standardized point of reference.

When inspection equipment interacts with a datum, it needs to contact it in a specific order to ensure that the measurements reflect the true position of features relative to one another. This correct sequence helps in maintaining uniformity in measurement practices and ensures that all inspectors or machines measure the part under the same conditions, thereby enhancing quality control.

The other options do not accurately pertain to the function of datums. They involve aspects like the manufacturing method, material selection, or anticipated wear, which are unrelated to the role of datums in defining reference frames for measurements. Understanding that datums primarily influence how parts are aligned and measured during inspections is crucial in GD&T practice.