This article shows how an eye diagram optical transceiver test pinpoints jitter, noise, and dispersion limits, helping network engineers and lab teams make decisions with measurable margin. Eye Width is the horizontal distance between the two crossing points of the eye diagram, defined as the time difference between the points where the upper and lower edges intersect (Crossing Points). It represents the time window during which the signal remains in a valid state during transitions. Use mask testing to verify that a displayed Eye Diagram complies with an industry-standard waveform shape. A mask is a template that consists of pass/fail regions on the PLTS display screen., but test results can differ between test instruments. In addition, some models may show unit-to-unit variation, causing inconsistent results.