Abstract: The disclosure of this invention relates to calorimeters and a process for operating a colorimeter. The colorimeter of the disclosure is controlled by a microprocessor which evaluates a predetermined radiation absorption curve for each sample. This is to be contrasted with the prior art wherein the test on a given sample evaluates only radiation absorption concentration points which are evaluated by the microprocessor. The colorimeter gives more accurate readings as a result of the fact that an absorption curve and its parameters are evaluated for each sample. The calorimeter uses multiple LEDs as a radiation source. The microprocessor further controls other functions of the colorimeter. A separate microprocessor may be used to control these other functions. The calorimeter and process of this invention are also useful in the analysis of samples for turbidity.