In certain applications, the ability to detect changes in color is critical for process control purposes. As the color of an analyte changes, so does the amount of light it absorbs. According to Beer’s law, the absorbance of light is proportional to the product of the concentration and the path length being measured. We have developed a top of the line photometer, when used in conjunction with either an external flow cell or a transmission probe, will rapidly detect color changes and present them, in AU, on the unit’s display screen.