Supplemental material to the article "Optical n(p, T_90) measurement suite 1: He, Ar, and N_2" by PF Egan and Y Yang in International Journal of Thermophysics 2023.The archive file contains research data and analysis scripts as follows: The n(p, T_90) dataset for helium. A Python script analyzes the data to produce the estimate of temperature-dependent compressibility, and reproduces Fig. 2 from the article. The n(p, T_90) dataset for argon. A Python script analyzes the data to determine T - T_90, and reproduces Fig. 3 from the article. Additionally, the output data T - T_90 (Table 2 in the article) are included in a separate text file, together with the estimated uncertainty in the determination. The Python script includes the further analysis undertaken on the nonlinear terms B and C to reproduce Fig. 6. The n(p, T_90) dataset for nitrogen. A Python script analyzes the data to reveal the temperature-dependence of polarizability, and reproduce Fig. 4. The script includes the further analysis undertaken on the nonlinear terms B and C to reproduce Fig. 7. A Python script uses argon and nitrogen results from the present work to reproduce Fig. 5, a graphical depiction of difference with literature for the second density virial coefficient B_p.