High Quality Content by WIKIPEDIA articles! Ring lasers with a perimeter larger than about 40 cm ("large" ring lasers) are extremely precise instruments capable of measuring phenomena in optics and gravitation such as details of Earth rotation, Fresnel drag, Lense-Thirring effect, gravitational waves, quantum-electrodynamic effects and other relativistic effects. A 243-day measurement involving a 16 m ring yielded the greatest resolution achieved so far by any known measurement device.