Differential Refractometer with Extended Range - The Evolution Continues! The Optilab® T-rEX™ (refractometer with EXtended range) is a Refractive Index detector with high detection power and a high dynamic range. Using a combination of cutting-edge semiconductor photodiode technology and proprietary computer algorithms, the Optilab T-rEX™ achieves an unprecedented combination of sensitivity and range. For example, there are no range or gain settings. The full range of instrument detection is always present, and the full sensitivity exists over the entire range.