System and program for measuring progressively the absorbance changes of a large number of aliquots from a plurality of different samples in a continuous processing mode. A plurality of routine samples are maintained in an ordered sequence in a sample tray which may be moved to a first sample pick up position. Emergency samples (stats) and controls (standards) are positioned in a second plurality of auxiliary positions which may be moved to a second sample position. A first and second plurality of reagents are maintained, moved to respective reagent pick up positions, picked up, moved and dispensed in respective dispensing positions by respective single reagent dispensing arms in a similar manner to the sample operation. The chemical reaction is then monitored by photometer means preferably having a plurality of photometric detectors such that radiation passes through each of the cuvettes and the fluids therein during each cycle of the system. Just prior to the sample dispensing position the cuvette is cleaned and tested to ensure that all the previously added fluids have been removed prior to receiving a new sample. Any one sample may be tested with different reagents or reagent mixtures in different aliquots placed in separate cuvettes at each wavelength as desired. Each sample aliquot and reagent mixture may be measured to determine the rate of the chemical reaction and the equilibrium or end point of the reaction or both, if desired. The array of cuvettes is continuous, because it is replenished at the end of each sequence prior to the addition of the new sample.