Which of the following is not a read-out system used to present eddy current test information?

Litmus paper does not serve as a read-out system for presenting eddy current test information because it is primarily used for measuring the pH level of a solution, which is unrelated to the principles of eddy current testing. Eddy current testing involves the use of electromagnetic induction to detect surface and near-surface defects in conductive materials. The information from such tests needs to be presented in a way that conveys the data quantitatively or qualitatively regarding the conductivity or material properties being tested.

Calibrated and uncalibrated meters, cathode ray tubes, and strip-chart recorders are all systems that can display readings and interpret the electrical signals that result from the eddy current tests. Calibrated meters provide accurate measurements by comparing results against known standards, while uncalibrated meters may give relative readings. Cathode ray tubes can present waveforms that relate to the eddy current response, and strip-chart recorders provide a visual representation over time, showing how the test results change as conditions vary. Each of these systems is relevant to the interpretation of data in the context of non-destructive testing, unlike litmus paper.