Ahmad, N., R. Radin Umar, I. Halim, M. Mohamed, M. R. Jamli, M. S. Baharudin, and M. Hamid. “Evaluation of Menu Hierarchy Display Types in Self-Checkout System: Effects on Human Performance”. Journal of Advanced Manufacturing Technology (JAMT), Vol. 12, no. 1(1), 1, pp. 371-82, https://jamt.utem.edu.my/jamt/article/view/4006.