Klett Bio Colorimeter, a device used in colorimetry to measure the absorbance of particular wavelengths of light by a specific solution. Colorimeters are commonly used to determine the concentration of a known solute in a given solution by the application of the Beer-Lambert law, which states that the concentration of a solute is proportional to the absorbance.

Klett Bio Colorimeters were specifically designed for clinical laboratory work. For example, they can be used to determine the concentration of hemoglobin, or other substances, in blood. This Klett colorimeter includes standard color disks made of glass, which can be used in place of standard solutions in color comparisons. The color disks are inserted into glass "plungers," similar to the glass sample cups, and viewed alongside the samples. The colorimeter's black metal base is attached to an upright made of hollow bronze and finished with black enamel which supports the microscope reader. Two stainless steel knobs on the upright control the height of the sample stand. The base supports a sliding metal and glass daylight filter and a blue glass color filter. The hollow base contains a light bulb and a hemoglobin results table, printed on linen, is built into the bottom front of the base and can be scrolled through with a black plastic knob.

Robert E. Klett, the inventor of this model, was a native of Berlin who immigrated to the U.S. in 1905. Klett established the Klett Manufacturing Co. in 1916. The company specialized in Duboscq-type colorimeters that, because of the war in Europe, were no longer available in the United States.