Mulia, M., S. Suardi, H. Susilo, F. K. Sinurat, and S. Supriadi. “Identification of Hardness Values of Boiler Pipes After Heating and Without Heating Process”. International Journal of Mechanical Computational and Manufacturing Research, vol. 13, no. 2, July 2024, pp. 50-56, https://trigin.pelnus.ac.id/index.php/Computational/article/view/177.