Anurattananon, C., P. Klomjit, A. Amaluk, N. Keereewan, and N. Choosombut. “Efficiency Improvement of Customer Service of Delivery Service System by Using Simulation: A Case Study of Sample Delivery Service Company”. Thai Industrial Engineering Network Journal, vol. 4, no. 2, Dec. 2018, pp. 59-69, https://ph02.tci-thaijo.org/index.php/ienj/article/view/176730.