The Fieldpiece RSO2 Replacement Oxygen (O2) Smart Sensor replaces the oxygen sensor within the SOX3 Combustion Checkers. This sensor is field-replaceable for an easy user installation in which replacement simply involves twisting the previous sensor out and new sensor in. No longer needing to send an instrument in just to replace the sensor and calibrate it minimizes downtime on the job. The pre-calibrated status offers more accurate readings once installed.