These Abbe refractometers provide highly accurate refractive index and Brix measurements of liquids and solids. Place your sample on the main prism, which is rimmed with stainless steel to prevent corrosion, look through the eyepiece and line up the shadowline in the crosshairs. The built-in 589 nm illuminator light source provides stable, monochromatic light (02939-00, -02 include LED light source), making it easy to read the black lines on the green field. The frosted secondary prism directs light to the main prism evenly, and lifts up for easy placement of solids and viscous liquids on the main prism. The color compensator knob allows you to adjust the boundary line for higher clarity and fine tuning capability for greater resolution. Use the color compensation knob and a conversion table to measure dispersion (variance of RI with different wavelengths of light). In order to maintain constant temperature at both prisms, these refractometers include four 9-mm OD ports (using 6 to 7-mm ID tubing) for connections to a constant-temperature bath. A thermistor thermometer for measuring temperature is built into the main prism. The temperature of the main prism is indicated on the LCD from 0 to 50°C with ±0.2°C accuracy; a digital temperature display unit is included. The built-in desiccant chamber removes moisture from internal optics ensuring an unobstructed view of scales.