... is single gas or composite gas with steady thermal conductivity value, such as air, N2, O2,CO2, etc. )CO20~100% (background ... is single gas or composite gas with steady thermal conductivity value, such as air, N2, O2, H2, etc.)He70~100% ( ... ) Other two kinds of gases with relatively big difference of thermal conductivity0-100% (refer to table of thermal conductivity value of gas)Precision±0.2 ...