Ubong, A. Iboh, et al. “Determination of the Density and Viscosity of Engine Oil With Grade 20w-50 in Nigeria”. International Journal of Natural and Practical Sciences (IJNPS), vol. 5, no. 1, Apr. 2023, pp. 1-11, http://icidr.org.ng/index.php/Ijnps/article/view/529.