M. Senthil Kumar, S. Kalaimathi, G. Karthik Rajan, S. Kathiravan, and M. Kavipriya. “No Queue Billing Purchase System”. International Journal of Intellectual Advancements and Research in Engineering Computations, vol. 6, no. 1, Mar. 2018, pp. 354-7, https://ijiarec.com/ijiarec/article/view/464.