These length testers use a round-robin method of measuring fiber length. You can measure cable length using a tape measure for accessible runs, but for cables already installed in walls, conduits, or buried underground, electronic methods are faster and far more accurate. The most common approach sends an electrical pulse down the cable and calculates length based on. Fiber optic cable length measurement depends on the context and desired precision. Several methods exist, ranging from simple approximations to highly accurate techniques used in manufacturing and installation. Two. Fiberlink 6658 Optical Length Tester offers a unique, low-cost alternative for users who need to measure the length of optical fibers. Rather than purchase certification. Can measure fibers less than 1 cm long The OZ Optics Optical Fiber Length Meter (OFLM-1000) delivers fast, accurate and reliable measurements of optical fiber lengths.