Which setting is often adjusted to ensure accurate distance measurements on an OTDR?

The index of refraction is a crucial setting in an Optical Time Domain Reflectometer (OTDR) because it directly affects the accuracy of distance measurements. The index of refraction is a measure of how much the speed of light is reduced in the medium (like fiber optic cable) compared to the speed of light in a vacuum. When light travels through fiber, it moves slower than in the vacuum due to the fiber material's optical properties.

The OTDR measures the time it takes for a light pulse to travel down the fiber, reflect off different points, and return to the unit. By using the index of refraction, the OTDR can convert the measured time into an accurate distance. If the wrong index value is used, the calculated distance could be significant, leading to errors in measuring the length of fibers or identifying the locations of faults.

This adjustment is essential because each type of fiber may have a different index of refraction based on its material and design. Hence, setting the correct index ensures that the distances reported by the OTDR reflect real-world measurements, which is crucial for effective troubleshooting and network management.