A colorimeter or photometer measures wavelength absorption in a solution in order to identify the level of a particular parameter. Several colorimeters can measure a variety of parameters while others are designed for a specific one. Most of the instruments are portable to be used in the field or the lab, and some are even waterproof. For a full COD (chemical oxygen demand) analysis, a thermoreactor will perform parameter thermal digestion tests to determine COD, total phosphate and total nitrogen.