Visual inspection identifies contamination, scratches, cracks, and endface defects that directly affect optical performance. This measurement is the basis for loss measurements as well as the power from a source or presented at a receiver. Power Meter Testing simulates the ay the cable will function with an actual link. As the components like fiber, connectors, splices, LED or laser sources, detectors and receivers are being developed, testing confirms their performance specifications and helps. To be able to judge whether a fiber optic cable plant is good, one does a insertion loss test with a light source and power meter and compares that to an estimate of what is a reasonable loss for that cable plant. The estimate, called a "loss budget" is calculated using typical component losses for. coming increasingly smaller. As a result, installers are finding out that previous methods and assumptions about fiber testing no longer hold true.