The Beaming Optical Length Tester (BOLT) and the Visual Optical Length Tester (VOLT) provide fast and precise measurements, making them a cost-effective alternative to more complex testing solutions. Several methods exist, ranging from simple approximations to highly accurate techniques used in manufacturing and installation. Loop length testing functions up to 1. As far as VFL function, VOLT holds its own against the best in the industry. Fiber installations are increasingly required to have fiber length measurements to comply with bid requirements. The OFLM delivers highly accurate optical light-path length. To measure something means to observe its characteristics and compare it to some standard "unit" of measurement.