Which of the following ensures accurate measurements when using an OTDR?

The correct answer is ensuring the fiber is clean and properly connected. This is crucial because the accuracy of measurements an Optical Time Domain Reflectometer (OTDR) provides heavily relies on the quality of the signal being transmitted through the fiber. Any dirt, dust, or improper connections can introduce loss and reflections that will distort the readings, leading to inaccurate assessments of the fiber's performance or condition.

A clean and well-connected fiber allows for a proper transmission of light, enabling the OTDR to detect changes in the signal that indicate issues such as breaks, splices, or bends in the fiber. Therefore, maintaining cleanliness and proper connection is essential for obtaining precise measurements, ensuring the reliability of results derived from the OTDR testing process.