Arnold S. Saputra, Yanditya E. Dwipada, Yoga A. Maulana, Emil R. Kaburuan*, Gunawan Wang. “The Effect of Online Gamification of Tutoring to Improve Student’s Achievement”. International Journal of Control and Automation, Vol. 13, no. 02, June 2020, pp. 1151 -58, http://sersc.org/journals/index.php/IJCA/article/view/26900.