Vogelman, J. H., E. Nieves, J.L. BRINO, R.A. Nash, and N. ORENTREICH. “A Spectrophotometric Method for Determining Relative SPF Values of Sunscreen Preparations”. Journal of Applied Cosmetology, vol. 3, no. 1, Mar. 1985, pp. 1-11, https://scientificeditorial.com/index.php/JAC/article/view/15.