The Matched Index of Refraction facility is the largest such facility in the world. Using light mineral oil, the facility allows researchers to use fused quartz models built to scale to study the flow of liquids inside and around objects with complicated geometries, such as the core of a nuclear reactor. The facility is basically a giant loop through which the mostly transparent oil is pumped at variable speeds. Special lasers perform "Doppler velocimetry", that produces a three-dimensional image allowing inspection of an object's flow properties. Observers can also watch the flow themselves through the polycarbonate viewing panes near the laser equipment.