The Fluke Networks FQM-100-M and FQM-M Fiber QuickMap measures length and identify high loss events on multimode fiber optic cable. Like an OTDR, a laser sends light pulses through the fiber and measures the power and timing of light reflected from high loss connections and splices, and the end of the fiber. VFLs work well for exposed lengths of fiber near a patch panel by illuminating bad connections and breaks. They are not very helpful for cable runs more than a few meters, or when the cable is not visible or accessible, or when the laser light can’t penetrate the jacket. Optical Time Domain Reflectometers (OTDR) provide graphical data and analysis along the entire length of a cable, way beyond the reach of a VFL, but they can be expensive and require more time and skill to operate.