Brix refractometers are often used by hobbyists for making preserves including jams, marmalades and honey. Multi-wavelength Abbe refractometers can be used to easily determine a sample's Abbe number. Differential refractometers are often used for the analysis of polymer samples in size exclusion chromatography. Automatic refractometers automatically measure the refractive index of a sample. Automatic refractometers are microprocessor-controlled electronic devices. The refractive index of liquids or solids can be measured with refractometers. Modern refractometers have the option of a built-in peristaltic pump. Another use around 1900 was as the light source in Pulfrich refractometers. Refractometers, which measure refractive indices, often use the critical angle. Refractometers are still commonly used for fruit juice.