Fiber optic test cords connect your tester to the fiber link you're testing and therefore act as a "window" into it. If that "window" is of poor quality or dirty , thenyour measurements will inaccurate. That's why Fluke Networks offers a wide array of test cords that match the quality of our instruments. These test cords will also work with other vendors' equipment, with exceptions noted below. (Always check your testers' documentation to ensure you're using acceptable test cords.)