An improved infrared analyzer is provided wherein an unknown specimen gas can be subjected to a measuring infrared ray and a comparative infrared ray to provide resulting signals. The system can be initially calibrated when a zero gas state is initially achieved in the sample cell, and correction factors are achieved by holding the zero gas instrument signal and an output difference between a zero gas comparison signal and the measuring signal for subsequent processing of the actual measurement of the specimen gas to provide a calibrated output signal representative of the concentration of the unknown gas.