What must be established prior to measuring loss when using the light source and power meter?

In fiber optics testing, before measuring loss with a light source and power meter, it is essential to establish a reference point or zero reference. This reference point serves as a baseline for the measurements you will take during the testing process. By determining the power level at the reference point, you can accurately gauge the amount of signal loss that occurs as the light travels through the fiber optic cable.

The zero reference allows for the differentiation between acceptable levels of attenuation and any potential issues that may arise within the fiber path, such as defects or poor connections. Without establishing this baseline, the measurements taken could be misleading, rendering them ineffective for proper troubleshooting or quality assurance.

While calibration standards, system checklists, and equipment logs are all important aspects of a well-organized fiber optic testing procedure, they do not directly pertain to the immediate requirement of establishing a baseline measurement for loss evaluation.