Abstract: A gas analyzer includes a cell adapted to receive a gas mixture and a source of infrared energy adapted to introduce the energy through the cell. A particular gas in the cell absorbs the portion of the energy so that an electrical gas signal is provided which has a magnitude dependent upon the percentage of concentration of the particular gas in the mixture. This gas signal is introduced through a variable resistance and compared with a reference signal to provide an output signal for driving a meter. Prior to the introduction of the gas mixture into the cell, the variable resistance can be adjusted with respect to the reference signal to provide the output signal with a zero magnitude for zeroing the meter. The parameters of the circuit automatically provide for the calibration of the span of the meter with the calibration of the zero of the meter.