Today I am reviewing the TPI 717 Combustion Flue Gas Analyzer series. The TPI 717 and TPI 717R are essentially the same device, but the TPI 717R uses a rechargeable Ni-MH battery, while the TPI 717 uses standard AA batteries. The TPI 717 series measures flue temperature, CO, and O2 and calculates efficiency, excess air, CO2, and CO/CO2 ratio.