The nitrogen product obtained from ambient temperature air separation usually contains nitrogen (N2), argon (Ar), oxygen (O2), and trace amounts of moisture. Due to the fact that the online analyzer (oxygen cell type or zirconia type) equipped with such devices can usually only analyze the oxygen content. Therefore, using the residual oxygen content in the product to represent the purity of nitrogen products is more direct and has not been converted in the analyzer or PLC. On the contrary, the analyzer that displays nitrogen content is calculated based on the following data: nitrogen purity=(1-oxygen content)%. Therefore, it is not a more direct display method, and it is easy to use the calculation process as a means to display inaccurate oxygen content.