You must establish the relationship between oxygen and carbon dioxide during the initial evaluation of your continuous emission monitoring systems. You may reestablish the relationship during annual evaluations. To establish the relationship use three procedures:(1) Use United States Environmental Protection Agency (EPA) Reference Method 3A or 3B in 40 Code of Federal Regulations (CFR) Part 60, Appendix A to determine oxygen concentration at the location of your carbon dioxide monitor.(2) Conduct at least three test runs for oxygen. Make sure each test run represents a 1-hour average and that sampling continues for at least 30 minutes in each hour.(3) Use the fuel-factor equation in EPA Reference Method 3B in 40 CFR Part 60, Appendix A to determine the relationship between oxygen and carbon dioxide.