Kimaiyo , P. J., et al. “ Construction of a Five-Level V-Dimensional Modified Third Order Rotatable Designs Using a Pair of Pairwise Balanced Designs ”. African Journal of Education,Science and Technology (AJEST), vol. 5, no. 3, Dec. 2019, pp. Pg 179 - 189, https://ajest.org/index.php/ajest/article/view/758.