In NDT, how is an "indication" defined?

In the context of nondestructive testing (NDT), an "indication" refers to a signal or response that suggests the presence of a discontinuity or flaw within the material being tested. This indication can arise from various methods used in NDT, such as ultrasonic testing, radiographic testing, or magnetic particle testing, among others. It serves as a critical piece of information for the inspector, indicating where further evaluation might be necessary to determine the significance of the flaw.

Essentially, the indication does not confirm the existence of a flaw outright; it prompts further investigation. The interpretation of these indications can lead to identifying critical defects that may compromise the integrity or safety of a material or structure. Therefore, this choice captures the essence of what indications represent in NDT—the initial evidence that warrants closer examination.

In contrast, the other options describe different aspects of the NDT process, such as the location of testing, preparation methods, or observations made by technicians, but they do not adequately capture the specific definition of an "indication" as it relates to detecting and evaluating flaws.